[DAGCombiner] Fix invalid alias analysis.

Summary:
When we know for sure whether two addresses do or do not alias, we
should immediately return from DAGCombiner::isAlias().

I think this comes from a bad copy/paste, Sorry for not catching that during the
code review.

Fixes PR41855.

Reviewers: niravd, gchatelet, EricWF

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61846

llvm-svn: 360566

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -6128,7 +6128,7 @@ static unsigned BigEndianByteAt(unsigned BW, unsigned i) {
 }
 
 // Check if the bytes offsets we are looking at match with either big or
-// little endian value loaded. Return true for big endian, false for little 
+// little endian value loaded. Return true for big endian, false for little
 // endian, and None if match failed.
 static Optional<bool> isBigEndian(const SmallVector<int64_t, 4> &ByteOffsets,
                                   int64_t FirstOffset) {
@@ -19800,8 +19800,7 @@ bool DAGCombiner::isAlias(SDNode *Op0, SDNode *Op1) const {
 
   bool IsAlias;
   if (BaseIndexOffset::computeAliasing(Op0, MUC0.NumBytes, Op1, MUC1.NumBytes,
-                                       DAG, IsAlias) &&
-      !IsAlias)
+                                       DAG, IsAlias))
     return IsAlias;
 
   // The following all rely on MMO0 and MMO1 being valid. Fail conservatively if

llvm/test/CodeGen/X86/lifetime-alias.ll

@@ -40,26 +40,28 @@ define dso_local i8 @main() local_unnamed_addr #0 personality i8* bitcast (i32 (
 ; CHECK-NEXT:    movl $1701999988, -{{[0-9]+}}(%rsp) # imm = 0x65727574
 ; CHECK-NEXT:    movb $0, -{{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    movaps %xmm0, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movabsq $1513209474796486656, %rax # imm = 0x1500000000000000
+; CHECK-NEXT:    movq $0, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb $21, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movabsq $7308613581744070988, %rax # imm = 0x656D69547473614C
 ; CHECK-NEXT:    movq %rax, -{{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    movups {{.*}}(%rip), %xmm1
 ; CHECK-NEXT:    movaps %xmm1, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movabsq $7308613581744070988, %rcx # imm = 0x656D69547473614C
-; CHECK-NEXT:    movq %rcx, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movabsq $792633534417207296, %rcx # imm = 0xB00000000000000
-; CHECK-NEXT:    movq %rcx, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movq -{{[0-9]+}}(%rsp), %rcx
-; CHECK-NEXT:    movq %rcx, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movzwl -{{[0-9]+}}(%rsp), %ecx
-; CHECK-NEXT:    movw %cx, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movb -{{[0-9]+}}(%rsp), %cl
-; CHECK-NEXT:    movb %cl, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movb -{{[0-9]+}}(%rsp), %cl
-; CHECK-NEXT:    movb %cl, -{{[0-9]+}}(%rsp)
-; CHECK-NEXT:    movl -{{[0-9]+}}(%rsp), %ecx
-; CHECK-NEXT:    movl %ecx, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb $0, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movabsq $792633534417207296, %rax # imm = 0xB00000000000000
+; CHECK-NEXT:    movq %rax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movq -{{[0-9]+}}(%rsp), %rax
+; CHECK-NEXT:    movq %rax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movzwl -{{[0-9]+}}(%rsp), %eax
+; CHECK-NEXT:    movw %ax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb -{{[0-9]+}}(%rsp), %al
+; CHECK-NEXT:    movb %al, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb -{{[0-9]+}}(%rsp), %al
+; CHECK-NEXT:    movb %al, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movl -{{[0-9]+}}(%rsp), %eax
+; CHECK-NEXT:    movl %eax, -{{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    movaps %xmm0, -{{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    movq $0, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movq -{{[0-9]+}}(%rsp), %rax
 ; CHECK-NEXT:    movq %rax, -{{[0-9]+}}(%rsp)
 ; CHECK-NEXT:    movaps -{{[0-9]+}}(%rsp), %xmm1
 ; CHECK-NEXT:    movups %xmm1, -{{[0-9]+}}(%rsp)