VirtRegRewriter checks for early clobbers before it reuses an available stack

slot.

Teach it to also check for early clobbered aliases, and early clobber operands
following the current operand.

This fixes the miscompilation in PR8044 where EC registers eax and ecx were
being used for inputs.

llvm-svn: 112988

1 files changed, 7 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/VirtRegRewriter.cpp b/llvm/lib/CodeGen/VirtRegRewriter.cpp
index 94a64ceec93..d988e106c52 100644
--- a/llvm/lib/CodeGen/VirtRegRewriter.cpp
+++ b/llvm/lib/CodeGen/VirtRegRewriter.cpp
@@ -2027,14 +2027,16 @@ LocalRewriter::RewriteMBB(LiveIntervals *LIs,
           CanReuse = !ReusedOperands.isClobbered(PhysReg) &&
             Spills.canClobberPhysReg(PhysReg);
         }
-        // If this is an asm, and PhysReg is used elsewhere as an earlyclobber
-        // operand, we can't also use it as an input.  (Outputs always come
-        // before inputs, so we can stop looking at i.)
+        // If this is an asm, and a PhysReg alias is used elsewhere as an
+        // earlyclobber operand, we can't also use it as an input.
         if (MI.isInlineAsm()) {
-          for (unsigned k=0; k<i; ++k) {
+          for (unsigned k = 0, e = MI.getNumOperands(); k != e; ++k) {
             MachineOperand &MOk = MI.getOperand(k);
-            if (MOk.isReg() && MOk.getReg()==PhysReg && MOk.isEarlyClobber()) {
+            if (MOk.isReg() && MOk.isEarlyClobber() &&
+                TRI->regsOverlap(MOk.getReg(), PhysReg)) {
               CanReuse = false;
+              DEBUG(dbgs() << "Not reusing physreg " << TRI->getName(PhysReg)
+                           << " for vreg" << VirtReg << ": " << MOk << '\n');
               break;
             }
           }