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SimplifyCFG: Enhance the "remove CFG edge that leads to null pointer dereference" optimization to also handle instructions with multiple uses.

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We conservatively only check the first use to avoid walking long use chains.
This catches the common case of having both a load and a store to a pointer
supplied by a PHI node.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165232 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-10-04 16:11:49 +00:00
parent 7508f946bc
commit 1e21db6e83
2 changed files with 31 additions and 2 deletions
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5
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -3786,11 +3786,12 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
if (!C)
return false;
if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
if (I->use_empty())
return false;
if (C->isNullValue()) {
Instruction *Use = I->use_back();
// Only look at the first use, avoid hurting compile time with long uselists
User *Use = *I->use_begin();
// Now make sure that there are no instructions in between that can alter
// control flow (eg. calls)

28
test/Transforms/SimplifyCFG/phi-undef-loadstore.ll
View File

@ -85,3 +85,31 @@ if.end7: ; preds = %if.else, %if.then4,
; CHECK: if.end7:
; CHECK: phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
}
define i32 @test4(i32* %a, i32 %b, i32* %c, i32 %d) nounwind {
entry:
%tobool = icmp eq i32 %b, 0
br i1 %tobool, label %if.else, label %if.then
if.then: ; preds = %entry
tail call void @bar() nounwind
br label %if.end7
if.else: ; preds = %entry
%tobool3 = icmp eq i32 %d, 0
br i1 %tobool3, label %if.end7, label %if.then4
if.then4: ; preds = %if.else
tail call void @bar() nounwind
br label %if.end7
if.end7: ; preds = %if.else, %if.then4, %if.then
%x.0 = phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
%gep = getelementptr i32* %x.0, i32 10
%tmp9 = load i32* %gep
%tmp10 = or i32 %tmp9, 1
store i32 %tmp10, i32* %gep
ret i32 %tmp9
; CHECK: @test4
; CHECK-NOT: phi
}