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[GVN] PRE of unordered loads

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Again, fairly simple.  Only change is ensuring that we actually copy the property of the load correctly.  The aliasing legality constraints were already handled by the FRE patches.  There's nothing special about unorder atomics from the perspective of the PRE algorithm itself.

llvm-svn: 268804
This commit is contained in:
Philip Reames 2016-05-06 21:43:51 +00:00
parent e784303c41
commit 751f932d9a
2 changed files with 113 additions and 8 deletions
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12
lib/Transforms/Scalar/GVN.cpp
View File

@ -1552,9 +1552,10 @@ bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
BasicBlock *UnavailablePred = PredLoad.first;
Value *LoadPtr = PredLoad.second;
Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
LI->getAlignment(),
UnavailablePred->getTerminator());
auto *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre",
LI->isVolatile(), LI->getAlignment(),
LI->getOrdering(), LI->getSynchScope(),
UnavailablePred->getTerminator());
// Transfer the old load's AA tags to the new load.
AAMDNodes Tags;
@ -1664,11 +1665,6 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
return true;
}
// This code hasn't been audited for atomic, ordered, or volatile memory
// access.
if (!LI->isSimple())
return false;
// Step 4: Eliminate partial redundancy.
if (!EnablePRE || !EnableLoadPRE)
return false;

109
test/Transforms/GVN/atomic.ll
View File

@ -392,3 +392,112 @@ next:
%res = sub i32 %a, %b
ret i32 %res
}
declare void @clobber()
; unordered atomic to unordered atomic
define i32 @non_local_pre(i32* %P1) {
; CHECK-LABEL: @non_local_pre(
; CHECK: load atomic i32, i32* %P1 unordered
; CHECK: load atomic i32, i32* %P1 unordered
; CHECK: %b = phi i32 [ %b.pre, %early ], [ %a, %0 ]
; CHECK: ret i32 %b
%a = load atomic i32, i32* %P1 unordered, align 4
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load atomic i32, i32* %P1 unordered, align 4
ret i32 %b
}
; unordered atomic to non-atomic
define i32 @non_local_pre2(i32* %P1) {
; CHECK-LABEL: @non_local_pre2(
; CHECK: load atomic i32, i32* %P1 unordered
; CHECK: load i32, i32* %P1
; CHECK: %b = phi i32 [ %b.pre, %early ], [ %a, %0 ]
; CHECK: ret i32 %b
%a = load atomic i32, i32* %P1 unordered, align 4
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load i32, i32* %P1
ret i32 %b
}
; non-atomic to unordered atomic - can't forward!
define i32 @non_local_pre3(i32* %P1) {
; CHECK-LABEL: @non_local_pre3(
; CHECK: %a = load i32, i32* %P1
; CHECK: %b = load atomic i32, i32* %P1 unordered
; CHECK: ret i32 %b
%a = load i32, i32* %P1
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load atomic i32, i32* %P1 unordered, align 4
ret i32 %b
}
; ordered atomic to ordered atomic - can't forward
define i32 @non_local_pre4(i32* %P1) {
; CHECK-LABEL: @non_local_pre4(
; CHECK: %a = load atomic i32, i32* %P1 seq_cst
; CHECK: %b = load atomic i32, i32* %P1 seq_cst
; CHECK: ret i32 %b
%a = load atomic i32, i32* %P1 seq_cst, align 4
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load atomic i32, i32* %P1 seq_cst, align 4
ret i32 %b
}
; can't remove volatile on any path
define i32 @non_local_pre5(i32* %P1) {
; CHECK-LABEL: @non_local_pre5(
; CHECK: %a = load atomic i32, i32* %P1 seq_cst
; CHECK: %b = load volatile i32, i32* %P1
; CHECK: ret i32 %b
%a = load atomic i32, i32* %P1 seq_cst, align 4
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load volatile i32, i32* %P1
ret i32 %b
}
; ordered atomic to unordered atomic
define i32 @non_local_pre6(i32* %P1) {
; CHECK-LABEL: @non_local_pre6(
; CHECK: load atomic i32, i32* %P1 seq_cst
; CHECK: load atomic i32, i32* %P1 unordered
; CHECK: %b = phi i32 [ %b.pre, %early ], [ %a, %0 ]
; CHECK: ret i32 %b
%a = load atomic i32, i32* %P1 seq_cst, align 4
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %early, label %next
early:
call void @clobber()
br label %next
next:
%b = load atomic i32, i32* %P1 unordered, align 4
ret i32 %b
}