[llvm-commits] [llvm] r138944 - in /llvm/trunk: lib/CodeGen/TargetInstrInfoImpl.cpp test/CodeGen/ARM/subreg-remat.ll

[Jakob Stoklund Olesen]

Author: stoklund
Date: Thu Sep  1 12:18:50 2011
New Revision: 138944

URL: http://llvm.org/viewvc/llvm-project?rev=138944&view=rev
Log:
Prevent remat of partial register redefinitions.

An instruction that redefines only part of a larger register can never
be rematerialized since the virtual register value depends on the old
value in other parts of the register.

This was fixed for the inline spiller in r138794.  This patch fixes the
problem for all register allocators, and includes a small test case.

<rdar://problem/10032939>

Added:
    llvm/trunk/test/CodeGen/ARM/subreg-remat.ll
Modified:
    llvm/trunk/lib/CodeGen/TargetInstrInfoImpl.cpp

Modified: llvm/trunk/lib/CodeGen/TargetInstrInfoImpl.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TargetInstrInfoImpl.cpp?rev=138944&r1=138943&r2=138944&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/TargetInstrInfoImpl.cpp (original)
+++ llvm/trunk/lib/CodeGen/TargetInstrInfoImpl.cpp Thu Sep  1 12:18:50 2011
@@ -362,6 +362,15 @@
   const TargetInstrInfo &TII = *TM.getInstrInfo();
   const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
 
+  // A sub-register definition can only be rematerialized if the instruction
+  // doesn't read the other parts of the register.  Otherwise it is really a
+  // read-modify-write operation on the full virtual register which cannot be
+  // moved safely.
+  unsigned Reg = MI->getOperand(0).getReg();
+  if (TargetRegisterInfo::isVirtualRegister(Reg) &&
+      MI->getOperand(0).getSubReg() && MI->readsVirtualRegister(Reg))
+    return false;
+
   // A load from a fixed stack slot can be rematerialized. This may be
   // redundant with subsequent checks, but it's target-independent,
   // simple, and a common case.

Added: llvm/trunk/test/CodeGen/ARM/subreg-remat.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/subreg-remat.ll?rev=138944&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/subreg-remat.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/subreg-remat.ll Thu Sep  1 12:18:50 2011
@@ -0,0 +1,28 @@
+; RUN: llc < %s -relocation-model=pic -disable-fp-elim -mcpu=cortex-a8 -pre-RA-sched=source | FileCheck %s
+target triple = "thumbv7-apple-ios"
+; <rdar://problem/10032939>
+;
+; The vector %v2 is built like this:
+;
+;   %vreg6:ssub_1<def> = VMOVSR %vreg0<kill>, pred:14, pred:%noreg, %vreg6<imp-def>; DPR_VFP2:%vreg6 GPR:%vreg0
+;   %vreg6:ssub_0<def> = VLDRS <cp#0>, 0, pred:14, pred:%noreg; mem:LD4[ConstantPool] DPR_VFP2:%vreg6
+;
+; When %vreg6 spills, the VLDRS constant pool load cannot be rematerialized
+; since it implicitly reads the ssub_1 sub-register.
+;
+; CHECK: f1
+; CHECK: vmov    s1, r0
+; CHECK: vldr.32 s0, LCPI
+; The vector must be spilled:
+; CHECK: vstr.64 d0,
+; CHECK: asm clobber d0
+; And reloaded after the asm:
+; CHECK: vldr.64 [[D16:d[0-9]+]],
+; CHECK: vstr.64 [[D16]], [r1]
+define void @f1(float %x, <2 x float>* %p) {
+  %v1 = insertelement <2 x float> undef, float %x, i32 1
+  %v2 = insertelement <2 x float> %v1, float 0x400921FB60000000, i32 0
+  %y = call double asm sideeffect "asm clobber $0", "=w,0,~{d1},~{d2},~{d3},~{d4},~{d5},~{d6},~{d7},~{d8},~{d9},~{d10},~{d11},~{d12},~{d13},~{d14},~{d15},~{d16},~{d17},~{d18},~{d19},~{d20},~{d21},~{d22},~{d23},~{d24},~{d25},~{d26},~{d27},~{d28},~{d29},~{d30},~{d31}"(<2 x float> %v2) nounwind
+  store <2 x float> %v2, <2 x float>* %p, align 8
+  ret void
+}