ARM: only form SMMLS when SUBE flags unused.

In this particular example we wouldn't want the smmls anyway (the value is
actually unused), but in general smmls does not provide the required flags
register so if that SUBE result is used we can't replace it.

llvm-svn: 277541

2 files changed, 23 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index ab20e4dee7b..d11de555fa3 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -3047,7 +3047,8 @@ void ARMDAGToDAGISel::Select(SDNode *N) {
     // Look for a pattern to match SMMLS
     // (sube a, (smul_loHi a, b), (subc 0, (smul_LOhi(a, b))))
     if (N->getOperand(1).getOpcode() != ISD::SMUL_LOHI ||
-        N->getOperand(2).getOpcode() != ARMISD::SUBC)
+        N->getOperand(2).getOpcode() != ARMISD::SUBC ||
+        !SDValue(N, 1).use_empty())
       break;
 
     if (Subtarget->isThumb())
diff --git a/llvm/test/CodeGen/ARM/smml.ll b/llvm/test/CodeGen/ARM/smml.ll
index 807445fcad9..1d6273ca204 100644
--- a/llvm/test/CodeGen/ARM/smml.ll
+++ b/llvm/test/CodeGen/ARM/smml.ll
@@ -44,3 +44,24 @@ entry:
   %conv3 = trunc i64 %shr7 to i32
   ret i32 %conv3
 }
+
+declare void @opaque(i32)
+define void @test_used_flags(i32 %in1, i32 %in2) {
+; CHECK-V7-LABEL: test_used_flags:
+; CHECK-V7: smull [[PROD_LO:r[0-9]+]], [[PROD_HI:r[0-9]+]], r0, r1
+; CHECK-V7: rsbs {{.*}}, [[PROD_LO]], #0
+; CHECK-V7: rscs {{.*}}, [[PROD_HI]], #0
+  %in1.64 = sext i32 %in1 to i64
+  %in2.64 = sext i32 %in2 to i64
+  %mul = mul nsw i64 %in1.64, %in2.64
+  %tst = icmp slt i64 %mul, 1
+  br i1 %tst, label %true, label %false
+
+true:
+  call void @opaque(i32 42)
+  ret void
+
+false:
+  call void @opaque(i32 56)
+  ret void
+}