[PowerPC] Report true displacement value from getPreIndexedAddressParts

DAGCombiner::CombineToPreIndexedLoadStore calls a target routine to
decompose a memory address into a base/offset pair.  It expects the
offset (if constant) to be the true displacement value in order to
perform optional additional optimizations; in particular, to convert
other uses of the original pointer into uses of the new base pointer
after pre-increment.

The PowerPC implementation of getPreIndexedAddressParts, however,
simply calls SelectAddressRegImm, which returns a TargetConstant.
This value is appropriate for encoding into the instruction, but
it is not always usable as true displacement value:

- Its type is always MVT::i32, even on 64-bit, where addresses
  ought to be i64 ... this causes the optimization to simply
  always fail on 64-bit due to this line in DAGCombiner:

      // FIXME: In some cases, we can be smarter about this.
      if (Op1.getValueType() != Offset.getValueType()) {

- Its value is truncated to an unsigned 16-bit value if negative.
  This causes the above opimization to generate wrong code.

This patch fixes both problems by simply returning the true
displacement value (in its original type).  This doesn't
affect any other user of the displacement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182012 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index 3e65606c43aec6d8802c47580fd14626d6cfcc38..84cf8f6a57617e36078b1425471a397599585ecb 100644 (file)
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -1061,7 +1061,7 @@ bool PPCTargetLowering::SelectAddressRegImm(SDValue N, SDValue &Disp,
   if (N.getOpcode() == ISD::ADD) {
     short imm = 0;
     if (isIntS16Immediate(N.getOperand(1), imm)) {
-      Disp = DAG.getTargetConstant((int)imm & 0xFFFF, MVT::i32);
+      Disp = DAG.getTargetConstant(imm, N.getValueType());
       if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(N.getOperand(0))) {
         Base = DAG.getTargetFrameIndex(FI->getIndex(), N.getValueType());
       } else {
@@ -1093,7 +1093,7 @@ bool PPCTargetLowering::SelectAddressRegImm(SDValue N, SDValue &Disp,
         // If all of the bits are known zero on the LHS or RHS, the add won't
         // carry.
         Base = N.getOperand(0);
-        Disp = DAG.getTargetConstant((int)imm & 0xFFFF, MVT::i32);
+        Disp = DAG.getTargetConstant(imm, N.getValueType());
         return true;
       }
     }

diff --git a/test/CodeGen/PowerPC/2013-05-15-preinc-fold.ll b/test/CodeGen/PowerPC/2013-05-15-preinc-fold.ll
new file mode 100644 (file)
index 0000000..b75337d
--- /dev/null
+++ b/test/CodeGen/PowerPC/2013-05-15-preinc-fold.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define i8* @test(i8* %base, i8 %val) {
+entry:
+  %arrayidx = getelementptr inbounds i8* %base, i32 -1
+  store i8 %val, i8* %arrayidx, align 1
+  %arrayidx2 = getelementptr inbounds i8* %base, i32 1
+  store i8 %val, i8* %arrayidx2, align 1
+  ret i8* %arrayidx
+}
+; CHECK: @test
+; CHECK: %entry
+; CHECK-NEXT: stbu 4, -1(3)
+; CHECK-NEXT: stb 4, 2(3)
+; CHECK-NEXT: blr
+