[llvm] c6fcd5d - [SelectionDAG] ComputeNumSignBits add getValidMaximumShiftAmountConstant() for ISD::SHL support
Simon Pilgrim via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 13 10:03:06 PST 2020
Author: Simon Pilgrim
Date: 2020-01-13T18:02:37Z
New Revision: c6fcd5d115b62280669719c5ead436904c93d6cb
URL: https://github.com/llvm/llvm-project/commit/c6fcd5d115b62280669719c5ead436904c93d6cb
DIFF: https://github.com/llvm/llvm-project/commit/c6fcd5d115b62280669719c5ead436904c93d6cb.diff
LOG: [SelectionDAG] ComputeNumSignBits add getValidMaximumShiftAmountConstant() for ISD::SHL support
Allows us to handle non-uniform SHL shifts to determine the minimum number of sign bits remaining (based off the maximum shift amount value)
Added:
Modified:
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
llvm/test/CodeGen/X86/known-signbits-vector.ll
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 54899ab92634..1b81e7de8a40 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2449,6 +2449,32 @@ getValidMinimumShiftAmountConstant(SDValue V, const APInt &DemandedElts) {
return MinShAmt;
}
+/// If a SHL/SRA/SRL node has constant vector shift amounts that are all less
+/// than the element bit-width of the shift node, return the maximum value.
+static const APInt *
+getValidMaximumShiftAmountConstant(SDValue V, const APInt &DemandedElts) {
+ unsigned BitWidth = V.getScalarValueSizeInBits();
+ auto *BV = dyn_cast<BuildVectorSDNode>(V.getOperand(1));
+ if (!BV)
+ return nullptr;
+ const APInt *MaxShAmt = nullptr;
+ for (unsigned i = 0, e = BV->getNumOperands(); i != e; ++i) {
+ if (!DemandedElts[i])
+ continue;
+ auto *SA = dyn_cast<ConstantSDNode>(BV->getOperand(i));
+ if (!SA)
+ return nullptr;
+ // Shifting more than the bitwidth is not valid.
+ const APInt &ShAmt = SA->getAPIntValue();
+ if (ShAmt.uge(BitWidth))
+ return nullptr;
+ if (MaxShAmt && MaxShAmt->uge(ShAmt))
+ continue;
+ MaxShAmt = &ShAmt;
+ }
+ return MaxShAmt;
+}
+
/// Determine which bits of Op are known to be either zero or one and return
/// them in Known. For vectors, the known bits are those that are shared by
/// every vector element.
@@ -3621,6 +3647,11 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
Tmp = ComputeNumSignBits(Op.getOperand(0), DemandedElts, Depth + 1);
if (ShAmt->ult(Tmp))
return Tmp - ShAmt->getZExtValue();
+ } else if (const APInt *ShAmt =
+ getValidMaximumShiftAmountConstant(Op, DemandedElts)) {
+ Tmp = ComputeNumSignBits(Op.getOperand(0), DemandedElts, Depth + 1);
+ if (ShAmt->ult(Tmp))
+ return Tmp - ShAmt->getZExtValue();
}
break;
case ISD::AND:
diff --git a/llvm/test/CodeGen/X86/known-signbits-vector.ll b/llvm/test/CodeGen/X86/known-signbits-vector.ll
index 8f662c17bd81..1d2afebe2676 100644
--- a/llvm/test/CodeGen/X86/known-signbits-vector.ll
+++ b/llvm/test/CodeGen/X86/known-signbits-vector.ll
@@ -257,45 +257,30 @@ define <4 x double> @signbits_sext_shuffle_sitofp(<4 x i32> %a0, <4 x i64> %a1)
define <2 x double> @signbits_sext_shl_sitofp(<2 x i16> %a0) nounwind {
; X86-LABEL: signbits_sext_shl_sitofp:
; X86: # %bb.0:
-; X86-NEXT: pushl %ebp
-; X86-NEXT: movl %esp, %ebp
-; X86-NEXT: andl $-8, %esp
-; X86-NEXT: subl $32, %esp
; X86-NEXT: vpmovsxwq %xmm0, %xmm0
; X86-NEXT: vpsllq $5, %xmm0, %xmm1
; X86-NEXT: vpsllq $11, %xmm0, %xmm0
-; X86-NEXT: vmovq %xmm0, {{[0-9]+}}(%esp)
-; X86-NEXT: vpshufd {{.*#+}} xmm0 = xmm1[2,3,0,1]
-; X86-NEXT: vmovq %xmm0, {{[0-9]+}}(%esp)
-; X86-NEXT: fildll {{[0-9]+}}(%esp)
-; X86-NEXT: fstpl {{[0-9]+}}(%esp)
-; X86-NEXT: fildll {{[0-9]+}}(%esp)
-; X86-NEXT: fstpl (%esp)
-; X86-NEXT: vmovsd {{.*#+}} xmm0 = mem[0],zero
-; X86-NEXT: vmovhps {{.*#+}} xmm0 = xmm0[0,1],mem[0,1]
-; X86-NEXT: movl %ebp, %esp
-; X86-NEXT: popl %ebp
+; X86-NEXT: vpblendw {{.*#+}} xmm0 = xmm0[0,1,2,3],xmm1[4,5,6,7]
+; X86-NEXT: vpshufd {{.*#+}} xmm0 = xmm0[0,2,2,3]
+; X86-NEXT: vcvtdq2pd %xmm0, %xmm0
; X86-NEXT: retl
;
; X64-AVX1-LABEL: signbits_sext_shl_sitofp:
; X64-AVX1: # %bb.0:
; X64-AVX1-NEXT: vpmovsxwq %xmm0, %xmm0
-; X64-AVX1-NEXT: vpsllq $11, %xmm0, %xmm1
-; X64-AVX1-NEXT: vpsllq $5, %xmm0, %xmm0
-; X64-AVX1-NEXT: vpextrq $1, %xmm0, %rax
-; X64-AVX1-NEXT: vcvtsi2sd %eax, %xmm2, %xmm0
-; X64-AVX1-NEXT: vcvtdq2pd %xmm1, %xmm1
-; X64-AVX1-NEXT: vunpcklpd {{.*#+}} xmm0 = xmm1[0],xmm0[0]
+; X64-AVX1-NEXT: vpsllq $5, %xmm0, %xmm1
+; X64-AVX1-NEXT: vpsllq $11, %xmm0, %xmm0
+; X64-AVX1-NEXT: vpblendw {{.*#+}} xmm0 = xmm0[0,1,2,3],xmm1[4,5,6,7]
+; X64-AVX1-NEXT: vpshufd {{.*#+}} xmm0 = xmm0[0,2,2,3]
+; X64-AVX1-NEXT: vcvtdq2pd %xmm0, %xmm0
; X64-AVX1-NEXT: retq
;
; X64-AVX2-LABEL: signbits_sext_shl_sitofp:
; X64-AVX2: # %bb.0:
; X64-AVX2-NEXT: vpmovsxwq %xmm0, %xmm0
; X64-AVX2-NEXT: vpsllvq {{.*}}(%rip), %xmm0, %xmm0
-; X64-AVX2-NEXT: vpextrq $1, %xmm0, %rax
-; X64-AVX2-NEXT: vcvtsi2sd %eax, %xmm1, %xmm1
+; X64-AVX2-NEXT: vpshufd {{.*#+}} xmm0 = xmm0[0,2,2,3]
; X64-AVX2-NEXT: vcvtdq2pd %xmm0, %xmm0
-; X64-AVX2-NEXT: vunpcklpd {{.*#+}} xmm0 = xmm0[0],xmm1[0]
; X64-AVX2-NEXT: retq
%1 = sext <2 x i16> %a0 to <2 x i64>
%2 = shl <2 x i64> %1, <i64 11, i64 5>
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