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llvm-mirror/test/Transforms/SROA/phi-and-select.ll
Chandler Carruth c205d0f3c2 [SROA] Fix a nasty pile of bugs to do with big-endian, different alloca 
types and loads, loads or stores widened past the size of an alloca,
etc.

This started off with a bug report about big-endian behavior with
bitfields and loads and stores to a { i32, i24 } struct. An initial
attempt to fix this was sent for review in D10357, but that didn't
really get to the root of the problem.

The core issue was that canConvertValue and convertValue in SROA were
handling different bitwidth integers by doing a zext of the integer. It
wouldn't do a trunc though, only a zext! This would in turn lead SROA to
form an i24 load from an i24 alloca, zext it to i32, and then use it.
This would at least produce the wrong value for big-endian systems.

One of my many false starts here was to correct the computation for
big-endian systems by shifting. But this doesn't actually work because
the original code has a 64-bit store to the entire 8 bytes, and a 32-bit
load of the last 4 bytes, and because the alloc size is 8 bytes, we
can't lose that last (least significant if bigendian) byte! The real
problem here is that we're forming an i24 load in SROA which is actually
not sufficiently wide to load all of the necessary bits here. The source
has an i32 load, and SROA needs to form that as well.

The straightforward way to do this is to disable the zext logic in
canConvertValue and convertValue, forcing us to actually load all
32-bits. This seems like a really good change, but it in turn breaks
several other parts of SROA.

First in the chain of knock-on failures, we had places where we were
doing integer-widening promotion even though some of the integer loads
or stores extended *past the end* of the alloca's memory! There was even
a comment about preventing this, but it only prevented the case where
the type had a different bit size from its store size. So I added checks
to handle the cases where we actually have a widened load or store and
to avoid trying to special integer widening promotion in those cases.

Second, we actually rely on the ability to promote in the face of loads
past the end of an alloca! This is important so that we can (for
example) speculate loads around PHI nodes to do more promotion. The bits
loaded are garbage, but as long as they aren't used and the alignment is
suitable high (which it wasn't in the test case!) this is "fine". And we
can't stop promoting here, lots of things stop working well if we do. So
we need to add specific logic to handle the extension (and truncation)
case, but *only* where that extension or truncation are over bytes that
*are outside the alloca's allocated storage* and thus totally bogus to
load or store.

And of course, once we add back this correct handling of extension or
truncation, we need to correctly handle bigendian systems to avoid
re-introducing the exact bug that started us off on this chain of misery
in the first place, but this time even more subtle as it only happens
along speculated loads atop a PHI node.

I've ported an existing test for PHI speculation to the big-endian test
file and checked that we get that part correct, and I've added several
more interesting big-endian test cases that should help check that we're
getting this correct.

Fun times.

llvm-svn: 242869
2015-07-22 03:32:42 +00:00

603 lines
16 KiB
LLVM
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; RUN: opt < %s -sroa -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n8:16:32:64"
define i32 @test1() {
; CHECK-LABEL: @test1(
entry:
%a = alloca [2 x i32]
; CHECK-NOT: alloca
%a0 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 0
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 0, i32* %a0
store i32 1, i32* %a1
%v0 = load i32, i32* %a0
%v1 = load i32, i32* %a1
; CHECK-NOT: store
; CHECK-NOT: load
%cond = icmp sle i32 %v0, %v1
br i1 %cond, label %then, label %exit
then:
br label %exit
exit:
%phi = phi i32* [ %a1, %then ], [ %a0, %entry ]
; CHECK: phi i32 [ 1, %{{.*}} ], [ 0, %{{.*}} ]
%result = load i32, i32* %phi
ret i32 %result
}
define i32 @test2() {
; CHECK-LABEL: @test2(
entry:
%a = alloca [2 x i32]
; CHECK-NOT: alloca
%a0 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 0
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 0, i32* %a0
store i32 1, i32* %a1
%v0 = load i32, i32* %a0
%v1 = load i32, i32* %a1
; CHECK-NOT: store
; CHECK-NOT: load
%cond = icmp sle i32 %v0, %v1
%select = select i1 %cond, i32* %a1, i32* %a0
; CHECK: select i1 %{{.*}}, i32 1, i32 0
%result = load i32, i32* %select
ret i32 %result
}
define i32 @test3(i32 %x) {
; CHECK-LABEL: @test3(
entry:
%a = alloca [2 x i32]
; CHECK-NOT: alloca
; Note that we build redundant GEPs here to ensure that having different GEPs
; into the same alloca partation continues to work with PHI speculation. This
; was the underlying cause of PR13926.
%a0 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 0
%a0b = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 0
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
%a1b = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 0, i32* %a0
store i32 1, i32* %a1
; CHECK-NOT: store
switch i32 %x, label %bb0 [ i32 1, label %bb1
i32 2, label %bb2
i32 3, label %bb3
i32 4, label %bb4
i32 5, label %bb5
i32 6, label %bb6
i32 7, label %bb7 ]
bb0:
br label %exit
bb1:
br label %exit
bb2:
br label %exit
bb3:
br label %exit
bb4:
br label %exit
bb5:
br label %exit
bb6:
br label %exit
bb7:
br label %exit
exit:
%phi = phi i32* [ %a1, %bb0 ], [ %a0, %bb1 ], [ %a0, %bb2 ], [ %a1, %bb3 ],
[ %a1b, %bb4 ], [ %a0b, %bb5 ], [ %a0b, %bb6 ], [ %a1b, %bb7 ]
; CHECK: phi i32 [ 1, %{{.*}} ], [ 0, %{{.*}} ], [ 0, %{{.*}} ], [ 1, %{{.*}} ], [ 1, %{{.*}} ], [ 0, %{{.*}} ], [ 0, %{{.*}} ], [ 1, %{{.*}} ]
%result = load i32, i32* %phi
ret i32 %result
}
define i32 @test4() {
; CHECK-LABEL: @test4(
entry:
%a = alloca [2 x i32]
; CHECK-NOT: alloca
%a0 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 0
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 0, i32* %a0
store i32 1, i32* %a1
%v0 = load i32, i32* %a0
%v1 = load i32, i32* %a1
; CHECK-NOT: store
; CHECK-NOT: load
%cond = icmp sle i32 %v0, %v1
%select = select i1 %cond, i32* %a0, i32* %a0
; CHECK-NOT: select
%result = load i32, i32* %select
ret i32 %result
; CHECK: ret i32 0
}
define i32 @test5(i32* %b) {
; CHECK-LABEL: @test5(
entry:
%a = alloca [2 x i32]
; CHECK-NOT: alloca
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 1, i32* %a1
; CHECK-NOT: store
%select = select i1 true, i32* %a1, i32* %b
; CHECK-NOT: select
%result = load i32, i32* %select
; CHECK-NOT: load
ret i32 %result
; CHECK: ret i32 1
}
declare void @f(i32*, i32*)
define i32 @test6(i32* %b) {
; CHECK-LABEL: @test6(
entry:
%a = alloca [2 x i32]
%c = alloca i32
; CHECK-NOT: alloca
%a1 = getelementptr [2 x i32], [2 x i32]* %a, i64 0, i32 1
store i32 1, i32* %a1
%select = select i1 true, i32* %a1, i32* %b
%select2 = select i1 false, i32* %a1, i32* %b
%select3 = select i1 false, i32* %c, i32* %b
; CHECK: %[[select2:.*]] = select i1 false, i32* undef, i32* %b
; CHECK: %[[select3:.*]] = select i1 false, i32* undef, i32* %b
; Note, this would potentially escape the alloca pointer except for the
; constant folding of the select.
call void @f(i32* %select2, i32* %select3)
; CHECK: call void @f(i32* %[[select2]], i32* %[[select3]])
%result = load i32, i32* %select
; CHECK-NOT: load
%dead = load i32, i32* %c
ret i32 %result
; CHECK: ret i32 1
}
define i32 @test7() {
; CHECK-LABEL: @test7(
; CHECK-NOT: alloca
entry:
%X = alloca i32
br i1 undef, label %good, label %bad
good:
%Y1 = getelementptr i32, i32* %X, i64 0
store i32 0, i32* %Y1
br label %exit
bad:
%Y2 = getelementptr i32, i32* %X, i64 1
store i32 0, i32* %Y2
br label %exit
exit:
%P = phi i32* [ %Y1, %good ], [ %Y2, %bad ]
; CHECK: %[[phi:.*]] = phi i32 [ 0, %good ],
%Z2 = load i32, i32* %P
ret i32 %Z2
; CHECK: ret i32 %[[phi]]
}
define i32 @test8(i32 %b, i32* %ptr) {
; Ensure that we rewrite allocas to the used type when that use is hidden by
; a PHI that can be speculated.
; CHECK-LABEL: @test8(
; CHECK-NOT: alloca
; CHECK-NOT: load
; CHECK: %[[value:.*]] = load i32, i32* %ptr
; CHECK-NOT: load
; CHECK: %[[result:.*]] = phi i32 [ undef, %else ], [ %[[value]], %then ]
; CHECK-NEXT: ret i32 %[[result]]
entry:
%f = alloca float
%test = icmp ne i32 %b, 0
br i1 %test, label %then, label %else
then:
br label %exit
else:
%bitcast = bitcast float* %f to i32*
br label %exit
exit:
%phi = phi i32* [ %bitcast, %else ], [ %ptr, %then ]
%loaded = load i32, i32* %phi, align 4
ret i32 %loaded
}
define i32 @test9(i32 %b, i32* %ptr) {
; Same as @test8 but for a select rather than a PHI node.
; CHECK-LABEL: @test9(
; CHECK-NOT: alloca
; CHECK-NOT: load
; CHECK: %[[value:.*]] = load i32, i32* %ptr
; CHECK-NOT: load
; CHECK: %[[result:.*]] = select i1 %{{.*}}, i32 undef, i32 %[[value]]
; CHECK-NEXT: ret i32 %[[result]]
entry:
%f = alloca float
store i32 0, i32* %ptr
%test = icmp ne i32 %b, 0
%bitcast = bitcast float* %f to i32*
%select = select i1 %test, i32* %bitcast, i32* %ptr
%loaded = load i32, i32* %select, align 4
ret i32 %loaded
}
define float @test10(i32 %b, float* %ptr) {
; Don't try to promote allocas which are not elligible for it even after
; rewriting due to the necessity of inserting bitcasts when speculating a PHI
; node.
; CHECK-LABEL: @test10(
; CHECK: %[[alloca:.*]] = alloca
; CHECK: %[[argvalue:.*]] = load float, float* %ptr
; CHECK: %[[cast:.*]] = bitcast double* %[[alloca]] to float*
; CHECK: %[[allocavalue:.*]] = load float, float* %[[cast]]
; CHECK: %[[result:.*]] = phi float [ %[[allocavalue]], %else ], [ %[[argvalue]], %then ]
; CHECK-NEXT: ret float %[[result]]
entry:
%f = alloca double
store double 0.0, double* %f
%test = icmp ne i32 %b, 0
br i1 %test, label %then, label %else
then:
br label %exit
else:
%bitcast = bitcast double* %f to float*
br label %exit
exit:
%phi = phi float* [ %bitcast, %else ], [ %ptr, %then ]
%loaded = load float, float* %phi, align 4
ret float %loaded
}
define float @test11(i32 %b, float* %ptr) {
; Same as @test10 but for a select rather than a PHI node.
; CHECK-LABEL: @test11(
; CHECK: %[[alloca:.*]] = alloca
; CHECK: %[[cast:.*]] = bitcast double* %[[alloca]] to float*
; CHECK: %[[allocavalue:.*]] = load float, float* %[[cast]]
; CHECK: %[[argvalue:.*]] = load float, float* %ptr
; CHECK: %[[result:.*]] = select i1 %{{.*}}, float %[[allocavalue]], float %[[argvalue]]
; CHECK-NEXT: ret float %[[result]]
entry:
%f = alloca double
store double 0.0, double* %f
store float 0.0, float* %ptr
%test = icmp ne i32 %b, 0
%bitcast = bitcast double* %f to float*
%select = select i1 %test, float* %bitcast, float* %ptr
%loaded = load float, float* %select, align 4
ret float %loaded
}
define i32 @test12(i32 %x, i32* %p) {
; Ensure we don't crash or fail to nuke dead selects of allocas if no load is
; never found.
; CHECK-LABEL: @test12(
; CHECK-NOT: alloca
; CHECK-NOT: select
; CHECK: ret i32 %x
entry:
%a = alloca i32
store i32 %x, i32* %a
%dead = select i1 undef, i32* %a, i32* %p
%load = load i32, i32* %a
ret i32 %load
}
define i32 @test13(i32 %x, i32* %p) {
; Ensure we don't crash or fail to nuke dead phis of allocas if no load is ever
; found.
; CHECK-LABEL: @test13(
; CHECK-NOT: alloca
; CHECK-NOT: phi
; CHECK: ret i32 %x
entry:
%a = alloca i32
store i32 %x, i32* %a
br label %loop
loop:
%phi = phi i32* [ %p, %entry ], [ %a, %loop ]
br i1 undef, label %loop, label %exit
exit:
%load = load i32, i32* %a
ret i32 %load
}
define i32 @test14(i1 %b1, i1 %b2, i32* %ptr) {
; Check for problems when there are both selects and phis and one is
; speculatable toward promotion but the other is not. That should block all of
; the speculation.
; CHECK-LABEL: @test14(
; CHECK: alloca
; CHECK: alloca
; CHECK: select
; CHECK: phi
; CHECK: phi
; CHECK: select
; CHECK: ret i32
entry:
%f = alloca i32
%g = alloca i32
store i32 0, i32* %f
store i32 0, i32* %g
%f.select = select i1 %b1, i32* %f, i32* %ptr
br i1 %b2, label %then, label %else
then:
br label %exit
else:
br label %exit
exit:
%f.phi = phi i32* [ %f, %then ], [ %f.select, %else ]
%g.phi = phi i32* [ %g, %then ], [ %ptr, %else ]
%f.loaded = load i32, i32* %f.phi
%g.select = select i1 %b1, i32* %g, i32* %g.phi
%g.loaded = load i32, i32* %g.select
%result = add i32 %f.loaded, %g.loaded
ret i32 %result
}
define i32 @PR13905() {
; Check a pattern where we have a chain of dead phi nodes to ensure they are
; deleted and promotion can proceed.
; CHECK-LABEL: @PR13905(
; CHECK-NOT: alloca i32
; CHECK: ret i32 undef
entry:
%h = alloca i32
store i32 0, i32* %h
br i1 undef, label %loop1, label %exit
loop1:
%phi1 = phi i32* [ null, %entry ], [ %h, %loop1 ], [ %h, %loop2 ]
br i1 undef, label %loop1, label %loop2
loop2:
br i1 undef, label %loop1, label %exit
exit:
%phi2 = phi i32* [ %phi1, %loop2 ], [ null, %entry ]
ret i32 undef
}
define i32 @PR13906() {
; Another pattern which can lead to crashes due to failing to clear out dead
; PHI nodes or select nodes. This triggers subtly differently from the above
; cases because the PHI node is (recursively) alive, but the select is dead.
; CHECK-LABEL: @PR13906(
; CHECK-NOT: alloca
entry:
%c = alloca i32
store i32 0, i32* %c
br label %for.cond
for.cond:
%d.0 = phi i32* [ undef, %entry ], [ %c, %if.then ], [ %d.0, %for.cond ]
br i1 undef, label %if.then, label %for.cond
if.then:
%tmpcast.d.0 = select i1 undef, i32* %c, i32* %d.0
br label %for.cond
}
define i64 @PR14132(i1 %flag) {
; CHECK-LABEL: @PR14132(
; Here we form a PHI-node by promoting the pointer alloca first, and then in
; order to promote the other two allocas, we speculate the load of the
; now-phi-node-pointer. In doing so we end up loading a 64-bit value from an i8
; alloca. While this is a bit dubious, we were asserting on trying to
; rewrite it. The trick is that the code using the value may carefully take
; steps to only use the not-undef bits, and so we need to at least loosely
; support this..
entry:
%a = alloca i64, align 8
%b = alloca i8, align 8
%ptr = alloca i64*, align 8
; CHECK-NOT: alloca
%ptr.cast = bitcast i64** %ptr to i8**
store i64 0, i64* %a, align 8
store i8 1, i8* %b, align 8
store i64* %a, i64** %ptr, align 8
br i1 %flag, label %if.then, label %if.end
if.then:
store i8* %b, i8** %ptr.cast, align 8
br label %if.end
; CHECK-NOT: store
; CHECK: %[[ext:.*]] = zext i8 1 to i64
if.end:
%tmp = load i64*, i64** %ptr, align 8
%result = load i64, i64* %tmp, align 8
; CHECK-NOT: load
; CHECK: %[[result:.*]] = phi i64 [ %[[ext]], %if.then ], [ 0, %entry ]
ret i64 %result
; CHECK-NEXT: ret i64 %[[result]]
}
define float @PR16687(i64 %x, i1 %flag) {
; CHECK-LABEL: @PR16687(
; Check that even when we try to speculate the same phi twice (in two slices)
; on an otherwise promotable construct, we don't get ahead of ourselves and try
; to promote one of the slices prior to speculating it.
entry:
%a = alloca i64, align 8
store i64 %x, i64* %a
br i1 %flag, label %then, label %else
; CHECK-NOT: alloca
; CHECK-NOT: store
; CHECK: %[[lo:.*]] = trunc i64 %x to i32
; CHECK: %[[shift:.*]] = lshr i64 %x, 32
; CHECK: %[[hi:.*]] = trunc i64 %[[shift]] to i32
then:
%a.f = bitcast i64* %a to float*
br label %end
; CHECK: %[[lo_cast:.*]] = bitcast i32 %[[lo]] to float
else:
%a.raw = bitcast i64* %a to i8*
%a.raw.4 = getelementptr i8, i8* %a.raw, i64 4
%a.raw.4.f = bitcast i8* %a.raw.4 to float*
br label %end
; CHECK: %[[hi_cast:.*]] = bitcast i32 %[[hi]] to float
end:
%a.phi.f = phi float* [ %a.f, %then ], [ %a.raw.4.f, %else ]
%f = load float, float* %a.phi.f
ret float %f
; CHECK: %[[phi:.*]] = phi float [ %[[lo_cast]], %then ], [ %[[hi_cast]], %else ]
; CHECK-NOT: load
; CHECK: ret float %[[phi]]
}
; Verifies we fixed PR20425. We should be able to promote all alloca's to
; registers in this test.
;
; %0 = slice
; %1 = slice
; %2 = phi(%0, %1) // == slice
define float @simplify_phi_nodes_that_equal_slice(i1 %cond, float* %temp) {
; CHECK-LABEL: @simplify_phi_nodes_that_equal_slice(
entry:
%arr = alloca [4 x float], align 4
; CHECK-NOT: alloca
br i1 %cond, label %then, label %else
then:
%0 = getelementptr inbounds [4 x float], [4 x float]* %arr, i64 0, i64 3
store float 1.000000e+00, float* %0, align 4
br label %merge
else:
%1 = getelementptr inbounds [4 x float], [4 x float]* %arr, i64 0, i64 3
store float 2.000000e+00, float* %1, align 4
br label %merge
merge:
%2 = phi float* [ %0, %then ], [ %1, %else ]
store float 0.000000e+00, float* %temp, align 4
%3 = load float, float* %2, align 4
ret float %3
}
; A slightly complicated example for PR20425.
;
; %0 = slice
; %1 = phi(%0) // == slice
; %2 = slice
; %3 = phi(%1, %2) // == slice
define float @simplify_phi_nodes_that_equal_slice_2(i1 %cond, float* %temp) {
; CHECK-LABEL: @simplify_phi_nodes_that_equal_slice_2(
entry:
%arr = alloca [4 x float], align 4
; CHECK-NOT: alloca
br i1 %cond, label %then, label %else
then:
%0 = getelementptr inbounds [4 x float], [4 x float]* %arr, i64 0, i64 3
store float 1.000000e+00, float* %0, align 4
br label %then2
then2:
%1 = phi float* [ %0, %then ]
store float 2.000000e+00, float* %1, align 4
br label %merge
else:
%2 = getelementptr inbounds [4 x float], [4 x float]* %arr, i64 0, i64 3
store float 3.000000e+00, float* %2, align 4
br label %merge
merge:
%3 = phi float* [ %1, %then2 ], [ %2, %else ]
store float 0.000000e+00, float* %temp, align 4
%4 = load float, float* %3, align 4
ret float %4
}
%struct.S = type { i32 }
; Verifies we fixed PR20822. We have a foldable PHI feeding a speculatable PHI
; which requires the rewriting of the speculated PHI to handle insertion
; when the incoming pointer is itself from a PHI node. We would previously
; insert a bitcast instruction *before* a PHI, producing an invalid module;
; make sure we insert *after* the first non-PHI instruction.
define void @PR20822() {
; CHECK-LABEL: @PR20822(
entry:
%f = alloca %struct.S, align 4
; CHECK: %[[alloca:.*]] = alloca
br i1 undef, label %if.end, label %for.cond
for.cond: ; preds = %for.cond, %entry
br label %if.end
if.end: ; preds = %for.cond, %entry
%f2 = phi %struct.S* [ %f, %entry ], [ %f, %for.cond ]
; CHECK: phi i32
; CHECK: %[[cast:.*]] = bitcast i32* %[[alloca]] to %struct.S*
phi i32 [ undef, %entry ], [ undef, %for.cond ]
br i1 undef, label %if.then5, label %if.then2
if.then2: ; preds = %if.end
br label %if.then5
if.then5: ; preds = %if.then2, %if.end
%f1 = phi %struct.S* [ undef, %if.then2 ], [ %f2, %if.end ]
; CHECK: phi {{.*}} %[[cast]]
store %struct.S undef, %struct.S* %f1, align 4
ret void
}
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