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fix rdar://8785296 - -fcatch-undefined-behavior generates inefficient code 

The basic issue is that isel (very reasonably!) expects conditional branches
to be folded, so CGP leaving around a bunch dead computation feeding
conditional branches isn't such a good idea.  Just fold branches on constants
into unconditional branches.

llvm-svn: 123526
This commit is contained in:
Chris Lattner 2011-01-15 07:36:13 +00:00
parent ee588defc6
commit 8df83c4a24
2 changed files with 7 additions and 1 deletions
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3
llvm/lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -1071,6 +1071,9 @@ bool CodeGenPrepare::OptimizeInst(Instruction *I) {
if (CallInst *CI = dyn_cast<CallInst>(I)) if (CallInst *CI = dyn_cast<CallInst>(I))
return OptimizeCallInst(CI); return OptimizeCallInst(CI);
if (isa<TerminatorInst>(I))
return ConstantFoldTerminator(I->getParent());
return false; return false;
} }

5
llvm/test/Transforms/CodeGenPrepare/basic.ll
View File

@ -4,13 +4,16 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
target triple = "x86_64-apple-darwin10.0.0" target triple = "x86_64-apple-darwin10.0.0"
; CHECK: @test1 ; CHECK: @test1
; objectsize should fold to a constant, which causes the branch to fold to an
; uncond branch.
; rdar://8785296
define i32 @test1(i8* %ptr) nounwind ssp noredzone align 2 { define i32 @test1(i8* %ptr) nounwind ssp noredzone align 2 {
entry: entry:
%0 = tail call i64 @llvm.objectsize.i64(i8* %ptr, i1 false) %0 = tail call i64 @llvm.objectsize.i64(i8* %ptr, i1 false)
%1 = icmp ugt i64 %0, 3 %1 = icmp ugt i64 %0, 3
br i1 %1, label %T, label %trap br i1 %1, label %T, label %trap
; CHECK: br i1 true, label ; CHECK: br label %T
trap: ; preds = %0, %entry trap: ; preds = %0, %entry
tail call void @llvm.trap() noreturn nounwind tail call void @llvm.trap() noreturn nounwind
unreachable unreachable