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llvm-mirror/test/Transforms/GVN/phi-translate.ll
Duncan Sands f7df28c1f5 GVN does simple propagation of conditions: when it sees a conditional
branch "br i1 %x, label %if_true, label %if_false" then it replaces
"%x" with "true" in places only reachable via the %if_true arm, and
with "false" in places only reachable via the %if_false arm.  Except
that actually it doesn't: if value numbering shows that %y is equal
to %x then, yes, %y will be turned into true/false in this way, but
any occurrences of %x itself are not transformed.  Fix this.  What's
more, it's often the case that %x is an equality comparison such as
"%x = icmp eq %A, 0", in which case every occurrence of %A that is
only reachable via the %if_true arm can be replaced with 0.  Implement
this and a few other variations on this theme.  This reduces the number
of lines of LLVM IR in "GCC as one big file" by 0.2%.  It has a bigger
impact on Ada code, typically reducing the number of lines of bitcode
by around 0.4% by removing repeated compiler generated checks.  Passes
the LLVM nightly testsuite and the Ada ACATS testsuite.

llvm-svn: 141177
2011-10-05 14:28:49 +00:00

32 lines
716 B
LLVM

; RUN: opt -basicaa -gvn -S < %s | FileCheck %s
target datalayout = "e-p:64:64:64"
; CHECK: @foo
; CHECK: entry.end_crit_edge:
; CHECK: %n.pre = load i32* %q.phi.trans.insert
; CHECK: then:
; CHECK: store i32 %z
; CHECK: end:
; CHECK: %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ]
; CHECK: ret i32 %n
@G = external global [100 x i32]
define i32 @foo(i32 %x, i32 %z) {
entry:
%tobool = icmp eq i32 %z, 0
br i1 %tobool, label %end, label %then
then:
%i = sext i32 %x to i64
%p = getelementptr [100 x i32]* @G, i64 0, i64 %i
store i32 %z, i32* %p
br label %end
end:
%j = sext i32 %x to i64
%q = getelementptr [100 x i32]* @G, i64 0, i64 %j
%n = load i32* %q
ret i32 %n
}