[PATCH] D20036: [InstCombine] Fold icmp eq/ne (udiv i32 A, B), 0 -> icmp ugt/ule B, A

[Chad Rosier via llvm-commits]

mcrosier retitled this revision from "[InstCombine] Fold icmp eq/ne (udiv i32 CI2, A), 0 -> icmp ugt/ule A, CI2" to "[InstCombine] Fold icmp eq/ne (udiv i32 A, B), 0 -> icmp ugt/ule B, A".
mcrosier updated the summary for this revision.
mcrosier updated this revision to Diff 56578.
mcrosier added a comment.

Address David's comments:
-Handle both constant and non-constant numerator.
-Add test with -1 numerator.


http://reviews.llvm.org/D20036

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/compare-udiv.ll

Index: test/Transforms/InstCombine/compare-udiv.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/compare-udiv.ll
@@ -0,0 +1,41 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+; CHECK-LABEL: @test1
+; CHECK: %cmp1 = icmp ugt i32 %d, %n
+define i1 @test1(i32 %n, i32 %d) {
+  %div = udiv i32 %n, %d
+  %cmp1 = icmp eq i32 %div, 0
+  ret i1 %cmp1
+}
+
+; CHECK-LABEL: @test2
+; CHECK: %cmp1 = icmp ugt i32 %d, 64
+define i1 @test2(i32 %d) {
+  %div = udiv i32 64, %d
+  %cmp1 = icmp eq i32 %div, 0
+  ret i1 %cmp1
+}
+
+; CHECK-LABEL: @test3
+; CHECK: %cmp1 = icmp ule i32 %d, %n
+define i1 @test3(i32 %n, i32 %d) {
+  %div = udiv i32 %n, %d
+  %cmp1 = icmp ne i32 %div, 0
+  ret i1 %cmp1
+}
+
+; CHECK-LABEL: @test4
+; CHECK: %cmp1 = icmp ult i32 %d, 65
+define i1 @test4(i32 %d) {
+  %div = udiv i32 64, %d
+  %cmp1 = icmp ne i32 %div, 0
+  ret i1 %cmp1
+}
+
+; CHECK-LABEL: @test5
+; CHECK: ret i1 true
+define i1 @test5(i32 %d) {
+  %div = udiv i32 -1, %d
+  %cmp1 = icmp ne i32 %div, 0
+  ret i1 %cmp1
+}
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3287,7 +3287,16 @@
         if (Instruction *Inst = FoldICmpCstShlCst(I, Op0, A, CI, CI2))
           return Inst;
       }
+      // (icmp eq/ne (udiv A, B), 0) -> (icmp ugt/ule i32 B, A)
+      if (CI->isZero() && match(Op0, m_UDiv(m_Value(A), m_Value(B)))) {
+        ICmpInst::Predicate Pred = I.getPredicate() == ICmpInst::ICMP_EQ
+                                       ? ICmpInst::ICMP_UGT
+                                       : ICmpInst::ICMP_ULE;
+        return new ICmpInst(Pred, B, A);
+      }
     }
+    // FIXME: Handle (icmp ugt (udiv i32 CI2, A), CI) and
+    // (icmp ult (udiv i32 CI2, A), CI).
 
     // If this comparison is a normal comparison, it demands all
     // bits, if it is a sign bit comparison, it only demands the sign bit.


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