[InstCombine] Simplify max(min(abs()))

[sergachev]

Remove smax from smax(smin(abs(x), y), 0) if y >= 0.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Ilia Sergachev (sergachev)

Changes

Remove smax from smax(smin(abs(x), y), 0) if y >= 0.

---

Full diff: https://github.com/llvm/llvm-project/pull/110997.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+7)
• (modified) llvm/test/Transforms/InstCombine/abs-intrinsic.ll (+22)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index f7a9406791801c..59b92bc833b673 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1770,6 +1770,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       }
     }
 
+    // smax(smin(abs(x), y), 0) -> smin(abs(x), y) where y >= 0
+    if (match(I0, m_SMin(m_c_Intrinsic<Intrinsic::abs>(m_Value(), m_Value()),
+                         m_NonNegative())) &&
+        match(I1, m_Zero())) {
+      return replaceInstUsesWith(*II, I0);
+    }
+
     // umin(i1 X, i1 Y) -> and i1 X, Y
     // smax(i1 X, i1 Y) -> and i1 X, Y
     if ((IID == Intrinsic::umin || IID == Intrinsic::smax) &&
diff --git a/llvm/test/Transforms/InstCombine/abs-intrinsic.ll b/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
index f7c639f1d8e6ba..53ad2057373569 100644
--- a/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
+++ b/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
@@ -847,3 +847,25 @@ cond.end:
   %r = phi i32 [ %0, %cond.true ], [ 0, %entry ]
   ret i32 %r
 }
+
+define i32 @test_abs_min_max_nonneg(i32 %0) {
+; CHECK-LABEL: @test_abs_min_max_nonneg(
+; CHECK-NEXT: call i32 @llvm.abs.i32
+; CHECK-NEXT: call i32 @llvm.smin.i32
+; CHECK-NOT: call i32 @llvm.smax.i32
+  %2 = call i32 @llvm.abs.i32(i32 %0, i1 false)
+  %3 = call i32 @llvm.smin.i32(i32 %2, i32 5)
+  %4 = call i32 @llvm.smax.i32(i32 %3, i32 0)
+  ret i32 %4
+}
+
+define i32 @test_abs_min_max_unknown(i32 %0, i32 %1) {
+; CHECK-LABEL: @test_abs_min_max_unknown(
+; CHECK-NEXT: call i32 @llvm.abs.i32
+; CHECK-NEXT: call i32 @llvm.smin.i32
+; CHECK-NEXT: call i32 @llvm.smax.i32
+  %3 = call i32 @llvm.abs.i32(i32 %0, i1 false)
+  %4 = call i32 @llvm.smin.i32(i32 %3, i32 %1)
+  %5 = call i32 @llvm.smax.i32(i32 %4, i32 0)
+  ret i32 %5
+}

[dtcxzyw]

It is incorrect when x==INT_MIN: https://alive2.llvm.org/ce/z/X4TZPY

BTW, isn't it already handled by CVP/SCCP?

[goldsteinn]

It is incorrect when x==INT_MIN: https://alive2.llvm.org/ce/z/X4TZPY

It is valid if you make INT_MIN ub.

[sergachev]

BTW, isn't it already handled by CVP/SCCP?

It isn't handled at the moment: https://alive2.llvm.org/ce/z/5o8Y-m

[goldsteinn]

Still need to be m_c_Intrinsic<..::abs>(m_Value(), m_One()) (And your tests will need toupdated correspondingly.)

[nikic]

BTW, isn't it already handled by CVP/SCCP?

It isn't handled at the moment: https://alive2.llvm.org/ce/z/5o8Y-m

It's not handled because the transform is incorrect. The variant with int_min_is_poison set is already handled: https://alive2.llvm.org/ce/z/Ah_8wT

[sergachev]

Thank you for the clarifications!