[X86] Allow x86 call frame optimization to fold more loads into pushes

This abstracts away the test for "when can we fold across a MachineInstruction"
into the the MI interface, and changes call-frame optimization use the same test
the peephole optimizer users.

Differential Revision: http://reviews.llvm.org/D11945

llvm-svn: 244729

3 files changed, 10 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index c3d58426277..e072ee1d6d5 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -1503,6 +1503,10 @@ bool MachineInstr::hasUnmodeledSideEffects() const {
   return false;
 }
 
+bool MachineInstr::isLoadFoldBarrier() const {
+  return mayStore() || isCall() || hasUnmodeledSideEffects();
+}
+
 /// allDefsAreDead - Return true if all the defs of this instruction are dead.
 ///
 bool MachineInstr::allDefsAreDead() const {
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 3dc73bac5b8..4d593543806 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -1234,9 +1234,9 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
       if (MI->isDebugValue())
           continue;
 
-      // If there exists an instruction which belongs to the following
-      // categories, we will discard the load candidates.
-      if (MI->mayStore() || MI->isCall() || MI->hasUnmodeledSideEffects())
+      // If we run into an instruction we can't fold across, discard
+      // the load candidates.
+      if (MI->isLoadFoldBarrier())
         FoldAsLoadDefCandidates.clear();
 
       if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() ||
diff --git a/llvm/lib/Target/X86/X86CallFrameOptimization.cpp b/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
index 4fdb89631a9..dd33c2e54b8 100644
--- a/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
+++ b/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
@@ -528,13 +528,10 @@ MachineInstr *X86CallFrameOptimization::canFoldIntoRegPush(
       DefMI->getParent() != FrameSetup->getParent())
     return nullptr;
 
-  // Now, make sure everything else up until the ADJCALLSTACK is a sequence
-  // of MOVs. To be less conservative would require duplicating a lot of the
-  // logic from PeepholeOptimizer.
-  // FIXME: A possibly better approach would be to teach the PeepholeOptimizer
-  // to be smarter about folding into pushes.
+  // Make sure we don't have any instructions between DefMI and the
+  // push that make folding the load illegal.
   for (auto I = DefMI; I != FrameSetup; ++I)
-    if (I->getOpcode() != X86::MOV32rm)
+    if (I->isLoadFoldBarrier())
       return nullptr;
 
   return DefMI;