[llvm] d0f8047 - [RISCV] Teach computeKnownBitsForTargetNode that VLENB will never be more than 65536/8.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2021-07-17T11:24:20-07:00
New Revision: d0f8047d37bf0543a4ef758213af9aec6143df41

URL: https://github.com/llvm/llvm-project/commit/d0f8047d37bf0543a4ef758213af9aec6143df41
DIFF: https://github.com/llvm/llvm-project/commit/d0f8047d37bf0543a4ef758213af9aec6143df41.diff

LOG: [RISCV] Teach computeKnownBitsForTargetNode that VLENB will never be more than 65536/8.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    llvm/test/CodeGen/RISCV/rvv/rvv-vscale.i64.ll

Removed: 
    


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diff  --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 05a1dbedeba8..e7ea2e16dcfe 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -6452,6 +6452,8 @@ void RISCVTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
   case RISCVISD::READ_VLENB:
     // We assume VLENB is at least 16 bytes.
     Known.Zero.setLowBits(4);
+    // We assume VLENB is no more than 65536 / 8 bytes.
+    Known.Zero.setBitsFrom(14);
     break;
   case ISD::INTRINSIC_W_CHAIN: {
     unsigned IntNo = Op.getConstantOperandVal(1);

diff  --git a/llvm/test/CodeGen/RISCV/rvv/rvv-vscale.i64.ll b/llvm/test/CodeGen/RISCV/rvv/rvv-vscale.i64.ll
index 29498ad5fcfe..615822235823 100644
--- a/llvm/test/CodeGen/RISCV/rvv/rvv-vscale.i64.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/rvv-vscale.i64.ll
@@ -50,9 +50,9 @@ define i64 @vscale_uimmpow2xlen() nounwind {
 ;
 ; RV32-LABEL: vscale_uimmpow2xlen:
 ; RV32:       # %bb.0: # %entry
-; RV32-NEXT:    csrr a1, vlenb
-; RV32-NEXT:    slli a0, a1, 3
-; RV32-NEXT:    srli a1, a1, 29
+; RV32-NEXT:    csrr a0, vlenb
+; RV32-NEXT:    slli a0, a0, 3
+; RV32-NEXT:    mv a1, zero
 ; RV32-NEXT:    ret
 entry:
   %0 = call i64 @llvm.vscale.i64()