[X86] Fix an 8 bit testb being selected when folding a volatile i32 load pattern.

Differential Revision: https://reviews.llvm.org/D71581

2 files changed, 44 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index 4e29597e941..3e2406e93f2 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -5146,6 +5146,17 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
       MachineSDNode *NewNode;
       SDValue Tmp0, Tmp1, Tmp2, Tmp3, Tmp4;
       if (tryFoldLoad(Node, N0.getNode(), Reg, Tmp0, Tmp1, Tmp2, Tmp3, Tmp4)) {
+        if (auto *LoadN = dyn_cast<LoadSDNode>(N0.getOperand(0).getNode())) {
+          if (!LoadN->isSimple()) {
+            unsigned NumVolBits = LoadN->getValueType(0).getSizeInBits();
+            if (MOpc == X86::TEST8mi && NumVolBits != 8)
+              break;
+            else if (MOpc == X86::TEST16mi && NumVolBits != 16)
+              break;
+            else if (MOpc == X86::TEST32mi && NumVolBits != 32)
+              break;
+          }
+        }
         SDValue Ops[] = { Tmp0, Tmp1, Tmp2, Tmp3, Tmp4, Imm,
                           Reg.getOperand(0) };
         NewNode = CurDAG->getMachineNode(MOpc, dl, MVT::i32, MVT::Other, Ops);
diff --git a/llvm/test/CodeGen/X86/select-testb-volatile-load.ll b/llvm/test/CodeGen/X86/select-testb-volatile-load.ll
new file mode 100644
index 00000000000..69cfe17b486
--- /dev/null
+++ b/llvm/test/CodeGen/X86/select-testb-volatile-load.ll
@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-apple-darwin < %s | FileCheck %s
+
+; This test checks that we don't try to narrow the volatile load by selecting
+; the pattern below into a testb instruction.
+
+define void @testb_volatile(i32 **%ptrptr) {
+; CHECK-LABEL: testb_volatile:
+; CHECK:       ## %bb.0: ## %entry
+; CHECK-NEXT:    movq (%rdi), %rax
+; CHECK-NEXT:    testl $1, (%rax)
+; CHECK-NEXT:    jne LBB0_1
+; CHECK-NEXT:  ## %bb.2: ## %exit
+; CHECK-NEXT:    movl $1, (%rax)
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  LBB0_1: ## %bb2
+; CHECK-NEXT:    movl $0, (%rax)
+; CHECK-NEXT:    retq
+entry:
+  %ptr = load i32*, i32** %ptrptr, align 8
+  %vol_load = load volatile i32, i32* %ptr, align 4
+  %and = and i32 %vol_load, 1
+  %cmp = icmp eq i32 %and, 0
+  br i1 %cmp, label %exit, label %bb2
+
+bb2:
+  store i32 0, i32 *%ptr, align 4
+  ret void
+
+exit:
+  store i32 1, i32 *%ptr, align 4
+  ret void
+}