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

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

Author: sergachev

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -1770,6 +1770,14 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       }
     }
 
+    // smax(smin(abs(x), y), 0) -> smin(abs(x), y) where y >= 0
+    if (IID == Intrinsic::smax &&
+        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) &&

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
+}