[llvm] 5692fc3 - [RISCV] Add a pattern for (sext_inreg (mul (and X, 0xffffffff), (and Y, 0xffffffff)), i32) to suppress MULW formation

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2021-03-27T15:37:18-07:00
New Revision: 5692fc38e0d17abc55a4a84da98f021a1d53d76d

URL: https://github.com/llvm/llvm-project/commit/5692fc38e0d17abc55a4a84da98f021a1d53d76d
DIFF: https://github.com/llvm/llvm-project/commit/5692fc38e0d17abc55a4a84da98f021a1d53d76d.diff

LOG: [RISCV] Add a pattern for (sext_inreg (mul (and X, 0xffffffff), (and Y, 0xffffffff)), i32) to suppress MULW formation

We have a special pattern for
(mul (and X, 0xffffffff), (and Y, 0xffffffff)), to optimize the
ANDs to shift. But if a sext_inreg coms first, we'll form a MULW
and limit the effectiveness of the special match. So this patch
adds a larger pattern to suppress the MULW formation by emitting
a sext.w and then the same output we use for the
(mul (and X, 0xffffffff), (and Y, 0xffffffff)). This should all
get CSEd.

This is the issue I was trying to fix with D99029, but that affected
many more tests.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVInstrInfoM.td
    llvm/test/CodeGen/RISCV/xaluo.ll

Removed: 
    


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diff  --git a/llvm/lib/Target/RISCV/RISCVInstrInfoM.td b/llvm/lib/Target/RISCV/RISCVInstrInfoM.td
index d6f8287f199c..e841d7fdea0b 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoM.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoM.td
@@ -104,4 +104,11 @@ let Predicates = [HasStdExtM, IsRV64, NotHasStdExtZba] in {
 // still be better off shifting both left by 32.
 def : Pat<(i64 (mul (and GPR:$rs1, 0xffffffff), (and GPR:$rs2, 0xffffffff))),
           (MULHU (SLLI GPR:$rs1, 32), (SLLI GPR:$rs2, 32))>;
+// Prevent matching the first part of this pattern to mulw. The mul here has
+// additionals users or the ANDs would have been removed. The above pattern
+// will be used for the other users. If we form a mulw we'll keep the ANDs alive
+// and they'll still become SLLI+SRLI.
+def : Pat<(sext_inreg (mul (and GPR:$rs1, 0xffffffff),
+                           (and GPR:$rs2, 0xffffffff)), i32),
+          (ADDIW (MULHU (SLLI GPR:$rs1, 32), (SLLI GPR:$rs2, 32)), 0)>;
 } // Predicates = [HasStdExtM, IsRV64, NotHasStdExtZba]

diff  --git a/llvm/test/CodeGen/RISCV/xaluo.ll b/llvm/test/CodeGen/RISCV/xaluo.ll
index b535fd93be76..707d1621d6ef 100644
--- a/llvm/test/CodeGen/RISCV/xaluo.ll
+++ b/llvm/test/CodeGen/RISCV/xaluo.ll
@@ -1045,13 +1045,11 @@ define signext i32 @umulo3.i32(i32 signext %0, i32 signext %1, i32* %2) {
 ; RV64-LABEL: umulo3.i32:
 ; RV64:       # %bb.0:
 ; RV64-NEXT:    slli a1, a1, 32
-; RV64-NEXT:    srli a3, a1, 32
 ; RV64-NEXT:    slli a0, a0, 32
-; RV64-NEXT:    srli a4, a0, 32
 ; RV64-NEXT:    mulhu a0, a0, a1
-; RV64-NEXT:    srli a0, a0, 32
-; RV64-NEXT:    snez a1, a0
-; RV64-NEXT:    mulw a0, a4, a3
+; RV64-NEXT:    srli a1, a0, 32
+; RV64-NEXT:    snez a1, a1
+; RV64-NEXT:    sext.w a0, a0
 ; RV64-NEXT:    sw a1, 0(a2)
 ; RV64-NEXT:    ret
 ;