[llvm] 419c694 - [SimplifyLibCalls] Remove over-eager early return in strlen optzns.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2020-08-27T15:19:45+01:00
New Revision: 419c6948df420dc2638e74a2b409e1d117256050

URL: https://github.com/llvm/llvm-project/commit/419c6948df420dc2638e74a2b409e1d117256050
DIFF: https://github.com/llvm/llvm-project/commit/419c6948df420dc2638e74a2b409e1d117256050.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
    llvm/test/Transforms/InstCombine/strlen-1.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 78a52c992e9f..34eb9e1b8124 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -693,8 +693,6 @@ Value *LibCallSimplifier::optimizeStringLength(CallInst *CI, IRBuilderBase &B,
                            Offset);
       }
     }
-
-    return nullptr;
   }
 
   // strlen(x?"foo":"bars") --> x ? 3 : 4

diff  --git a/llvm/test/Transforms/InstCombine/strlen-1.ll b/llvm/test/Transforms/InstCombine/strlen-1.ll
index e9a6e714acd0..61bc2e57b08d 100644
--- a/llvm/test/Transforms/InstCombine/strlen-1.ll
+++ b/llvm/test/Transforms/InstCombine/strlen-1.ll
@@ -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