Use a 8 bit immediate when possible.

This fixes pr21529.

llvm-svn: 221700

2 files changed, 29 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 70487a11b39..6e6bedbc5fb 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -82,6 +82,17 @@ static unsigned getADDriOpcode(unsigned IsLP64, int64_t Imm) {
   }
 }
 
+static unsigned getANDriOpcode(bool IsLP64, int64_t Imm) {
+  if (IsLP64) {
+    if (isInt<8>(Imm))
+      return X86::AND64ri8;
+    return X86::AND64ri32;
+  }
+  if (isInt<8>(Imm))
+    return X86::AND32ri8;
+  return X86::AND32ri;
+}
+
 static unsigned getLEArOpcode(unsigned IsLP64) {
   return IsLP64 ? X86::LEA64r : X86::LEA32r;
 }
@@ -657,11 +668,12 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF) const {
   // able to calculate their offsets from the frame pointer).
   if (RegInfo->needsStackRealignment(MF)) {
     assert(HasFP && "There should be a frame pointer if stack is realigned.");
+    uint64_t Val = -MaxAlign;
     MachineInstr *MI =
       BuildMI(MBB, MBBI, DL,
-              TII.get(Uses64BitFramePtr ? X86::AND64ri32 : X86::AND32ri), StackPtr)
+              TII.get(getANDriOpcode(Uses64BitFramePtr, Val)), StackPtr)
       .addReg(StackPtr)
-      .addImm(-MaxAlign)
+      .addImm(Val)
       .setMIFlag(MachineInstr::FrameSetup);
 
     // The EFLAGS implicit def is dead.
diff --git a/llvm/test/CodeGen/X86/pr21529.ll b/llvm/test/CodeGen/X86/pr21529.ll
new file mode 100644
index 00000000000..9da73dd4095
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr21529.ll
@@ -0,0 +1,15 @@
+; RUN: llc -filetype=obj < %s | llvm-objdump -d - | FileCheck %s
+
+; Test that the direct object emission selects the and variant with 8 bit
+; immediate.
+; We used to get this wrong when using direct object emission, but not when
+; reading assembly.
+
+; CHECK: 48 83 e4 e0                    andq      $-32, %rsp
+
+target triple = "x86_64-pc-linux"
+
+define void @f() {
+  %foo = alloca i8, align 32
+  ret void
+}