[llvm] aef44e4 - [InstSimplify] Add simplification for `({u,s}rem (mul {nuw,nsw} X, C1), C0)`

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2024-07-01T22:22:36+08:00
New Revision: aef44e49a7b79cfaf4d7c09133ba7c30ddfdfdc7

URL: https://github.com/llvm/llvm-project/commit/aef44e49a7b79cfaf4d7c09133ba7c30ddfdfdc7
DIFF: https://github.com/llvm/llvm-project/commit/aef44e49a7b79cfaf4d7c09133ba7c30ddfdfdc7.diff

LOG: [InstSimplify] Add simplification for `({u,s}rem (mul {nuw,nsw} X, C1), C0)`

We can simplify these to `0` if `C1 % C0 == 0`

Proofs: https://alive2.llvm.org/ce/z/EejAdk

Closes #97037

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/rem.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index cdcc40c596b77..1b72f151e3692 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1226,13 +1226,29 @@ static Value *simplifyRem(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
     return V;
 
   // (X << Y) % X -> 0
-  if (Q.IIQ.UseInstrInfo &&
-      ((Opcode == Instruction::SRem &&
-        match(Op0, m_NSWShl(m_Specific(Op1), m_Value()))) ||
-       (Opcode == Instruction::URem &&
-        match(Op0, m_NUWShl(m_Specific(Op1), m_Value())))))
-    return Constant::getNullValue(Op0->getType());
+  if (Q.IIQ.UseInstrInfo) {
+    if ((Opcode == Instruction::SRem &&
+         match(Op0, m_NSWShl(m_Specific(Op1), m_Value()))) ||
+        (Opcode == Instruction::URem &&
+         match(Op0, m_NUWShl(m_Specific(Op1), m_Value()))))
+      return Constant::getNullValue(Op0->getType());
 
+    const APInt *C0;
+    if (match(Op1, m_APInt(C0))) {
+      // (srem (mul nsw X, C1), C0) -> 0 if C1 s% C0 == 0
+      // (urem (mul nuw X, C1), C0) -> 0 if C1 u% C0 == 0
+      if (Opcode == Instruction::SRem
+              ? match(Op0,
+                      m_NSWMul(m_Value(), m_CheckedInt([C0](const APInt &C) {
+                                 return C.srem(*C0).isZero();
+                               })))
+              : match(Op0,
+                      m_NUWMul(m_Value(), m_CheckedInt([C0](const APInt &C) {
+                                 return C.urem(*C0).isZero();
+                               }))))
+        return Constant::getNullValue(Op0->getType());
+    }
+  }
   return nullptr;
 }
 

diff  --git a/llvm/test/Transforms/InstSimplify/rem.ll b/llvm/test/Transforms/InstSimplify/rem.ll
index ad9cb21a12cc9..aceb7cb12185d 100644
--- a/llvm/test/Transforms/InstSimplify/rem.ll
+++ b/llvm/test/Transforms/InstSimplify/rem.ll
@@ -491,9 +491,7 @@ define i8 @urem_mul_sdiv(i8 %x, i8 %y) {
 
 define <2 x i8> @simplfy_srem_of_mul(<2 x i8> %x) {
 ; CHECK-LABEL: @simplfy_srem_of_mul(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw <2 x i8> [[X:%.*]], <i8 20, i8 10>
-; CHECK-NEXT:    [[R:%.*]] = srem <2 x i8> [[MUL]], <i8 5, i8 5>
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    ret <2 x i8> zeroinitializer
 ;
   %mul = mul nsw <2 x i8> %x, <i8 20, i8 10>
   %r = srem <2 x i8> %mul, <i8 5, i8 5>
@@ -513,9 +511,7 @@ define <2 x i8> @simplfy_srem_of_mul_fail_bad_mod(<2 x i8> %x) {
 
 define i8 @simplfy_urem_of_mul(i8 %x) {
 ; CHECK-LABEL: @simplfy_urem_of_mul(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nuw i8 [[X:%.*]], 30
-; CHECK-NEXT:    [[R:%.*]] = urem i8 [[MUL]], 10
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ;
   %mul = mul nuw i8 %x, 30
   %r = urem i8 %mul, 10