[PATCH] D22314: Make X86CallFrameOptimization work with code generated by fast isel.

[Nico Weber via llvm-commits]

thakis created this revision.
thakis added reviewers: mkuper, rnk.
thakis added a subscriber: llvm-commits.
Herald added a subscriber: aemerson.

My motivation is that I want to enable fast isel for thiscall and other callee-pop calls, but that currently means codegen stops creating pushls, which means test/CodeGen/X86/win32_sret.ll starts failing (harmlesly) with the fast isel change, and updating it to have to different expectations is harder than just teaching this pass about fast isel code -- and this fixes a TODO too.

http://reviews.llvm.org/D22314

Files:
  lib/Target/X86/X86CallFrameOptimization.cpp
  test/CodeGen/X86/fast-isel-call.ll

Index: test/CodeGen/X86/fast-isel-call.ll
===================================================================
--- test/CodeGen/X86/fast-isel-call.ll
+++ test/CodeGen/X86/fast-isel-call.ll
@@ -22,12 +22,12 @@
   call void @foo2(%struct.s* byval %d )
   ret void
 ; CHECK-LABEL: test2:
-; CHECK: movl	(%eax)
-; CHECK: movl {{.*}}, (%esp)
-; CHECK: movl	4(%eax)
-; CHECK: movl {{.*}}, 4(%esp)
-; CHECK: movl	8(%eax)
-; CHECK: movl {{.*}}, 8(%esp)
+; CHECK: movl	(%eax), %[[reg1:e[a-d]x]]
+; CHECK: movl	4(%eax), %[[reg2:e[a-d]x]]
+; CHECK: movl	8(%eax), %[[reg3:e[a-d]x]]
+; CHECK: pushl %[[reg3]]
+; CHECK: pushl %[[reg2]]
+; CHECK: pushl %[[reg1]]
 }
 
 declare void @llvm.memset.p0i8.i32(i8* nocapture, i8, i32, i32, i1) nounwind
Index: lib/Target/X86/X86CallFrameOptimization.cpp
===================================================================
--- lib/Target/X86/X86CallFrameOptimization.cpp
+++ lib/Target/X86/X86CallFrameOptimization.cpp
@@ -346,15 +346,15 @@
   while (I->getOpcode() == X86::LEA32r)
     ++I;
 
-  // We expect a copy instruction here.
-  // TODO: The copy instruction is a lowering artifact.
-  //       We should also support a copy-less version, where the stack
-  //       pointer is used directly.
-  if (!I->isCopy() || !I->getOperand(0).isReg())
-    return;
-  Context.SPCopy = &*I++;
-
-  unsigned StackPtr = Context.SPCopy->getOperand(0).getReg();
+  unsigned StackPtr = RegInfo.getStackRegister();
+  // SelectionDAG (but not FastISel) inserts a copy of ESP into a virtual
+  // register here.  If it's there, use that virtual register as stack pointer
+  // instead.
+  if (I->isCopy() && I->getOperand(0).isReg() && I->getOperand(1).isReg() &&
+      I->getOperand(1).getReg() == StackPtr) {
+    Context.SPCopy = &*I++;
+    StackPtr = Context.SPCopy->getOperand(0).getReg();
+  }
 
   // Scan the call setup sequence for the pattern we're looking for.
   // We only handle a simple case - a sequence of store instructions that
@@ -539,7 +539,7 @@
 
   // The stack-pointer copy is no longer used in the call sequences.
   // There should not be any other users, but we can't commit to that, so:
-  if (MRI->use_empty(Context.SPCopy->getOperand(0).getReg()))
+  if (Context.SPCopy && MRI->use_empty(Context.SPCopy->getOperand(0).getReg()))
     Context.SPCopy->eraseFromParent();
 
   // Once we've done this, we need to make sure PEI doesn't assume a reserved


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