[X86] Enable forwarding bool arguments in tail calls (PR26305)

zmodem · zmodem · commit 153e4b0f11f4 · 2016-03-03T02:06:32.000Z
The code was previously not able to track a boolean argument at a call site back to the formal argument of the caller. Differential Revision: http://reviews.llvm.org/D17786 llvm-svn: 262575
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3645,6 +3645,26 @@ bool MatchingStackOffset(SDValue Arg, unsigned Offset, ISD::ArgFlagsTy Flags,
                          MachineFrameInfo *MFI, const MachineRegisterInfo *MRI,
                          const X86InstrInfo *TII, const CCValAssign &VA) {
   unsigned Bytes = Arg.getValueType().getSizeInBits() / 8;
+
+  for (;;) {
+    // Look through nodes that don't alter the bits of the incoming value.
+    unsigned Op = Arg.getOpcode();
+    if (Op == ISD::ZERO_EXTEND || Op == ISD::ANY_EXTEND || Op == ISD::BITCAST) {
+      Arg = Arg.getOperand(0);
+      continue;
+    }
+    if (Op == ISD::TRUNCATE) {
+      const SDValue &TruncInput = Arg.getOperand(0);
+      if (TruncInput.getOpcode() == ISD::AssertZext &&
+          cast<VTSDNode>(TruncInput.getOperand(1))->getVT() ==
+              Arg.getValueType()) {
+        Arg = TruncInput.getOperand(0);
+        continue;
+      }
+    }
+    break;
+  }
+
   int FI = INT_MAX;
   if (Arg.getOpcode() == ISD::CopyFromReg) {
     unsigned VR = cast<RegisterSDNode>(Arg.getOperand(1))->getReg();
diff --git a/llvm/test/CodeGen/X86/tail-call-casts.ll b/llvm/test/CodeGen/X86/tail-call-casts.ll
@@ -0,0 +1,27 @@
+; RUN: llc -mtriple=i686-unknown-linux-gnu -o - %s | FileCheck %s
+
+declare void @g_bool(i1 zeroext)
+define void @f_bool(i1 zeroext %x) {
+entry:
+  tail call void @g_bool(i1 zeroext %x)
+  ret void
+
+; Forwarding a bool in a tail call works.
+; CHECK-LABEL: f_bool:
+; CHECK-NOT:   movz
+; CHECK:       jmp g_bool
+}
+
+
+declare void @g_float(float)
+define void @f_i32(i32 %x) {
+entry:
+  %0 = bitcast i32 %x to float
+  tail call void @g_float(float %0)
+  ret void
+
+; Forwarding a bitcasted value works too.
+; CHECK-LABEL: f_i32
+; CHECK-NOT:   mov
+; CHECK:       jmp g_float
+}
