[llvm] 1605593 - [SimplifyLibCalls] Fix memchr opt to use CreateLogicalAnd

[Juneyoung Lee via llvm-commits]

Author: Juneyoung Lee
Date: 2021-06-26T05:59:35+09:00
New Revision: 160559344026824ee0b510741c7906c0e165f9a7

URL: https://github.com/llvm/llvm-project/commit/160559344026824ee0b510741c7906c0e165f9a7
DIFF: https://github.com/llvm/llvm-project/commit/160559344026824ee0b510741c7906c0e165f9a7.diff

LOG: [SimplifyLibCalls] Fix memchr opt to use CreateLogicalAnd

This fixes a bug at LibCallSimplifier::optimizeMemChr which does the following transformation:

```
// memchr("\r\n", C, 2) != nullptr -> (1 << C & ((1 << '\r') | (1 << '\n')))
// != 0
//   after bounds check.
```

As written above, a bounds check on C (whether it is less than integer bitwidth) is done before doing `1 << C` otherwise 1 << C will overflow.
If the bounds check is false, the result of (1 << C & ...) must not be used at all, otherwise the result of shift (which is poison) will contaminate the whole results.
A correct way to encode this is `select i1 (bounds check), (1 << C & ...), false`  because select does not allow the unused operand to contaminate the result.
However, this optimization was introducing `and (bounds check), (1 << C & ...)` which cannot do that.

The bug was found from compilation of this C++ code: https://reviews.llvm.org/rG2fd3037ac615#1007197

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D104901

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 1589bb5d5fd4..0f8c4b8b5ae2 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -933,7 +933,8 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilderBase &B) {
 
     // Finally merge both checks and cast to pointer type. The inttoptr
     // implicitly zexts the i1 to intptr type.
-    return B.CreateIntToPtr(B.CreateAnd(Bounds, Bits, "memchr"), CI->getType());
+    return B.CreateIntToPtr(B.CreateLogicalAnd(Bounds, Bits, "memchr"),
+                            CI->getType());
   }
 
   // Check if all arguments are constants.  If so, we can constant fold.

diff  --git a/llvm/test/Transforms/InstCombine/memchr.ll b/llvm/test/Transforms/InstCombine/memchr.ll
index 2ea0121ec738..f3659882c98a 100644
--- a/llvm/test/Transforms/InstCombine/memchr.ll
+++ b/llvm/test/Transforms/InstCombine/memchr.ll
@@ -137,7 +137,7 @@ define i1 @test11(i32 %C) {
 ; CHECK-NEXT:    [[TMP3:%.*]] = shl i16 1, [[TMP2]]
 ; CHECK-NEXT:    [[TMP4:%.*]] = and i16 [[TMP3]], 9216
 ; CHECK-NEXT:    [[MEMCHR_BITS:%.*]] = icmp ne i16 [[TMP4]], 0
-; CHECK-NEXT:    [[MEMCHR:%.*]] = and i1 [[MEMCHR_BOUNDS]], [[MEMCHR_BITS]]
+; CHECK-NEXT:    [[MEMCHR:%.*]] = select i1 [[MEMCHR_BOUNDS]], i1 [[MEMCHR_BITS]], i1 false
 ; CHECK-NEXT:    ret i1 [[MEMCHR]]
 ;
   %dst = call i8* @memchr(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @newlines, i64 0, i64 0), i32 %C, i32 2)
@@ -164,7 +164,7 @@ define i1 @test13(i32 %C) {
 ; CHECK-NEXT:    [[TMP2:%.*]] = shl i32 1, [[TMP1]]
 ; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], -2147483647
 ; CHECK-NEXT:    [[MEMCHR_BITS:%.*]] = icmp ne i32 [[TMP3]], 0
-; CHECK-NEXT:    [[MEMCHR:%.*]] = and i1 [[MEMCHR_BOUNDS]], [[MEMCHR_BITS]]
+; CHECK-NEXT:    [[MEMCHR:%.*]] = select i1 [[MEMCHR_BOUNDS]], i1 [[MEMCHR_BITS]], i1 false
 ; CHECK-NEXT:    ret i1 [[MEMCHR]]
 ;
   %dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 2)

diff  --git a/llvm/test/Transforms/InstCombine/strchr-1.ll b/llvm/test/Transforms/InstCombine/strchr-1.ll
index 95bd7f7fbed5..ad924761fa58 100644
--- a/llvm/test/Transforms/InstCombine/strchr-1.ll
+++ b/llvm/test/Transforms/InstCombine/strchr-1.ll
@@ -95,7 +95,7 @@ define i1 @test_simplify7(i32 %C) {
 ; CHECK-NEXT:    [[TMP3:%.*]] = shl i16 1, [[TMP2]]
 ; CHECK-NEXT:    [[TMP4:%.*]] = and i16 [[TMP3]], 9217
 ; CHECK-NEXT:    [[MEMCHR_BITS:%.*]] = icmp ne i16 [[TMP4]], 0
-; CHECK-NEXT:    [[MEMCHR1:%.*]] = and i1 [[MEMCHR_BOUNDS]], [[MEMCHR_BITS]]
+; CHECK-NEXT:    [[MEMCHR1:%.*]] = select i1 [[MEMCHR_BOUNDS]], i1 [[MEMCHR_BITS]], i1 false
 ; CHECK-NEXT:    ret i1 [[MEMCHR1]]
 ;