[llvm] goldsteinn/rem of mul simpl (PR #97037)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: None (goldsteinn)

<details>
<summary>Changes</summary>

- **[InstSimplify] Add test for simplifying `({u,s}rem (mul {nuw,nsw} X, C1), C0)`; NFC**
- **[InstSimplify] Add simplification for `({u,s}rem (mul {nuw,nsw} X, C1), C0)`**


---
Full diff: https://github.com/llvm/llvm-project/pull/97037.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+13) 
- (modified) llvm/test/Transforms/InstSimplify/rem.ll (+55-2) 


``````````diff
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index cdcc40c596b77..446f97ebbc1ea 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1233,6 +1233,19 @@ static Value *simplifyRem(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
         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 a46db0342042f..cee0e0e346fc3 100644
--- a/llvm/test/Transforms/InstSimplify/rem.ll
+++ b/llvm/test/Transforms/InstSimplify/rem.ll
@@ -265,12 +265,14 @@ define i32 @rem4() {
 ; CHECK-NEXT:    [[CALL:%.*]] = call i32 @external(), !range [[RNG0:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[CALL]]
 ;
-  %call = call i32 @external(), !range !0
+  %call = call i32 @external() , !range !0
   %urem = urem i32 %call, 3
   ret i32 %urem
 }
 
-!0 = !{i32 0, i32 3}
+!0 = ! {
+i32 0, i32 3
+}
 
 define i32 @rem5(i32 %x, i32 %y) {
 ; CHECK-LABEL: @rem5(
@@ -488,3 +490,54 @@ define i8 @urem_mul_sdiv(i8 %x, i8 %y) {
   %mod = urem i8 %mul, %y
   ret i8 %mod
 }
+
+define <2 x i8> @simplfy_srem_of_mul(<2 x i8> %x) {
+; CHECK-LABEL: @simplfy_srem_of_mul(
+; 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>
+  ret <2 x i8> %r
+}
+
+define <2 x i8> @simplfy_srem_of_mul_fail_bad_mod(<2 x i8> %x) {
+; CHECK-LABEL: @simplfy_srem_of_mul_fail_bad_mod(
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw <2 x i8> [[X:%.*]], <i8 20, i8 11>
+; CHECK-NEXT:    [[R:%.*]] = srem <2 x i8> [[MUL]], <i8 5, i8 5>
+; CHECK-NEXT:    ret <2 x i8> [[R]]
+;
+  %mul = mul nsw <2 x i8> %x, <i8 20, i8 11>
+  %r = srem <2 x i8> %mul, <i8 5, i8 5>
+  ret <2 x i8> %r
+}
+
+define i8 @simplfy_urem_of_mul(i8 %x) {
+; CHECK-LABEL: @simplfy_urem_of_mul(
+; CHECK-NEXT:    ret i8 0
+;
+  %mul = mul nuw i8 %x, 30
+  %r = urem i8 %mul, 10
+  ret i8 %r
+}
+
+define i8 @simplfy_urem_of_mul_fail_bad_flag(i8 %x) {
+; CHECK-LABEL: @simplfy_urem_of_mul_fail_bad_flag(
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[X:%.*]], 30
+; CHECK-NEXT:    [[R:%.*]] = urem i8 [[MUL]], 10
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %mul = mul nsw i8 %x, 30
+  %r = urem i8 %mul, 10
+  ret i8 %r
+}
+
+define i8 @simplfy_urem_of_mul_fail_bad_mod(i8 %x) {
+; CHECK-LABEL: @simplfy_urem_of_mul_fail_bad_mod(
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[X:%.*]], 31
+; CHECK-NEXT:    [[R:%.*]] = urem i8 [[MUL]], 10
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %mul = mul nsw i8 %x, 31
+  %r = urem i8 %mul, 10
+  ret i8 %r
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/97037