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[SimplifyLibCalls] Remove over-eager early return in strlen optzns. 

Currently we bail out early for strlen calls with a GEP operand, if none
of the GEP specific optimizations fire. But there could be later
optimizations that still apply,  which we currently miss out on.

An example is that we do not apply the following optimization
   strlen(x) == 0 --> *x == 0

Unless I am missing something, there seems to be no reason for bailing
out early there.

Fixes PR47149.

Reviewed By: lebedev.ri, xbolva00

Differential Revision: https://reviews.llvm.org/D85886
This commit is contained in:
Florian Hahn 2020-08-27 14:13:07 +01:00
parent 5b2b754565
commit 419c6948df
2 changed files with 3 additions and 7 deletions
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2
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -693,8 +693,6 @@ Value *LibCallSimplifier::optimizeStringLength(CallInst *CI, IRBuilderBase &B,
Offset);
}
}
return nullptr;
}
// strlen(x?"foo":"bars") --> x ? 3 : 4

8
llvm/test/Transforms/InstCombine/strlen-1.ll
View File

@ -223,9 +223,7 @@ define i32 @test2(i8* %str) #0 {
define i1 @strlen0_after_write_to_first_byte_global() {
; CHECK-LABEL: @strlen0_after_write_to_first_byte_global(
; CHECK-NEXT: store i8 49, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @a, i32 0, i32 0), align 16
; CHECK-NEXT: [[LEN:%.*]] = tail call i32 @strlen(i8* nonnull dereferenceable(1) getelementptr inbounds ([32 x i8], [32 x i8]* @a, i32 0, i32 0))
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LEN]], 0
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 false
;
store i8 49, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @a, i64 0, i64 0), align 16
%len = tail call i32 @strlen(i8* nonnull dereferenceable(1) getelementptr inbounds ([32 x i8], [32 x i8]* @a, i64 0, i64 0))
@ -236,8 +234,8 @@ define i1 @strlen0_after_write_to_first_byte_global() {
define i1 @strlen0_after_write_to_second_byte_global() {
; CHECK-LABEL: @strlen0_after_write_to_second_byte_global(
; CHECK-NEXT: store i8 49, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @a, i32 0, i32 1), align 16
; CHECK-NEXT: [[LEN:%.*]] = tail call i32 @strlen(i8* nonnull dereferenceable(1) getelementptr inbounds ([32 x i8], [32 x i8]* @a, i32 0, i32 0))
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LEN]], 0
; CHECK-NEXT: [[STRLENFIRST:%.*]] = load i8, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @a, i32 0, i32 0), align 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[STRLENFIRST]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
store i8 49, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @a, i64 0, i64 1), align 16