ARM: don't mangle DAG constant if it has more than one use
The basic optimisation was to convert (mul $LHS, $complex_constant) into
roughly "(shl (mul $LHS, $simple_constant), $simple_amt)" when it was expected
to be cheaper. The original logic checks that the mul only has one use (since
we're mangling $complex_constant), but when used in even more complex
addressing modes there may be an outer addition that can pick up the wrong
value too.
I *think* the ARM addressing-mode problem is actually unreachable at the
moment, but that depends on complex assessments of the profitability of
pre-increment addressing modes so I've put a real check in there instead of an
assertion.
llvm-svn: 259228
diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index 9ffed03..89e0bab 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -747,7 +747,7 @@
// If Offset is a multiply-by-constant and it's profitable to extract a shift
// and use it in a shifted operand do so.
- if (Offset.getOpcode() == ISD::MUL) {
+ if (Offset.getOpcode() == ISD::MUL && N.hasOneUse()) {
unsigned PowerOfTwo = 0;
SDValue NewMulConst;
if (canExtractShiftFromMul(Offset, 31, PowerOfTwo, NewMulConst)) {
@@ -1422,7 +1422,7 @@
// If OffReg is a multiply-by-constant and it's profitable to extract a shift
// and use it in a shifted operand do so.
- if (OffReg.getOpcode() == ISD::MUL) {
+ if (OffReg.getOpcode() == ISD::MUL && N.hasOneUse()) {
unsigned PowerOfTwo = 0;
SDValue NewMulConst;
if (canExtractShiftFromMul(OffReg, 3, PowerOfTwo, NewMulConst)) {
diff --git a/llvm/test/CodeGen/ARM/shifter_operand.ll b/llvm/test/CodeGen/ARM/shifter_operand.ll
index 5d44eb0..e5f9b11 100644
--- a/llvm/test/CodeGen/ARM/shifter_operand.ll
+++ b/llvm/test/CodeGen/ARM/shifter_operand.ll
@@ -239,3 +239,20 @@
store i32 %add, i32* %addr
ret void
}
+
+define { i32, i32 } @test_multi_use_add(i32 %base, i32 %offset) {
+; CHECK-LABEL: test_multi_use_add:
+; CHECK-THUMB: movs [[CONST:r[0-9]+]], #28
+; CHECK-THUMB: movt [[CONST]], #1
+
+ %prod = mul i32 %offset, 65564
+ %sum = add i32 %base, %prod
+
+ %ptr = inttoptr i32 %sum to i32*
+ %loaded = load i32, i32* %ptr
+
+ %ret.tmp = insertvalue { i32, i32 } undef, i32 %sum, 0
+ %ret = insertvalue { i32, i32 } %ret.tmp, i32 %loaded, 1
+
+ ret { i32, i32 } %ret
+}