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Fold strlen(expr ? "str1" : "str2") to x ? len1 : len2. This fires about 330 times in a bootstrap of clang. 

llvm-svn: 207828
This commit is contained in:
Nick Lewycky 2014-05-02 04:11:45 +00:00
parent 0e363b75a4
commit 718ada97bc
2 changed files with 27 additions and 0 deletions
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15
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -784,10 +784,25 @@ struct StrLenOpt : public LibCallOptimization {
if (uint64_t Len = GetStringLength(Src))
return ConstantInt::get(CI->getType(), Len-1);
// strlen(x?"foo":"bars") --> x ? 3 : 4
if (SelectInst *SI = dyn_cast<SelectInst>(Src)) {
uint64_t LenTrue = GetStringLength(SI->getTrueValue());
uint64_t LenFalse = GetStringLength(SI->getFalseValue());
if (LenTrue && LenFalse) {
Context->emitOptimizationRemark(
"simplify-libcalls", *Caller, SI->getDebugLoc(),
"folded strlen(select) to select of constants");
return B.CreateSelect(SI->getCondition(),
ConstantInt::get(CI->getType(), LenTrue-1),
ConstantInt::get(CI->getType(), LenFalse-1));
}
}
// strlen(x) != 0 --> *x != 0
// strlen(x) == 0 --> *x == 0
if (isOnlyUsedInZeroEqualityComparison(CI))
return B.CreateZExt(B.CreateLoad(Src, "strlenfirst"), CI->getType());
return nullptr;
}
};

12
llvm/test/Transforms/InstCombine/strlen-1.ll
View File

@ -5,6 +5,7 @@
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
@hello = constant [6 x i8] c"hello\00"
@longer = constant [7 x i8] c"longer\00"
@null = constant [1 x i8] zeroinitializer
@null_hello = constant [7 x i8] c"\00hello\00"
@nullstring = constant i8 0
@ -85,6 +86,17 @@ define i1 @test_simplify8() {
; CHECK-NEXT: ret i1 false
}
define i32 @test_simplify9(i1 %x) {
; CHECK-LABEL: @test_simplify9
%hello = getelementptr [6 x i8]* @hello, i32 0, i32 0
%longer = getelementptr [7 x i8]* @longer, i32 0, i32 0
%s = select i1 %x, i8* %hello, i8* %longer
%l = call i32 @strlen(i8* %s)
; CHECK-NEXT: select i1 %x, i32 5, i32 6
ret i32 %l
; CHECK-NEXT: ret
}
; Check cases that shouldn't be simplified.
define i32 @test_no_simplify1() {