[PATCH] D21397: Teach SimplifyCFG to Create Switches from InstCombine Or Mask'd Comparisons

[Thomas Jablin via llvm-commits]

tjablin updated the summary for this revision.
tjablin updated this revision to Diff 61059.
tjablin added a comment.

I have split out and applied the bug fix and m_ConstantInt => m_APInt portions of the past separately. What remains is just the new functionality.


http://reviews.llvm.org/D21397

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/switch_create.ll

Index: test/Transforms/SimplifyCFG/switch_create.ll
===================================================================
--- test/Transforms/SimplifyCFG/switch_create.ll
+++ test/Transforms/SimplifyCFG/switch_create.ll
@@ -618,4 +618,43 @@
 
 else:
   ret void
+}
+
+; Form a switch when or'ing a power of two
+; CHECK-LABEL: define void @test21
+; CHECK: i32 32, label %else
+; CHECK: i32 13, label %else
+; CHECK: i32 12, label %else
+define void @test21(i32 %arg) {
+  %and = or i32 %arg, 1
+  %cmp1 = icmp ne i32 %and, 13
+  %cmp2 = icmp ne i32 %arg, 32
+  %pred = and i1 %cmp1, %cmp2
+  br i1 %pred, label %if, label %else
+
+if:
+  call void @foo1()
+  ret void
+
+else:
+  ret void
+}
+
+; Since %cmp1 is always false, a switch is never formed
+; CHECK-LABEL: define void @test22
+; CHECK-NOT: switch
+; CHECK: ret void
+define void @test22(i32 %arg) {
+  %and = or i32 %arg, 1
+  %cmp1 = icmp ne i32 %and, 12
+  %cmp2 = icmp ne i32 %arg, 32
+  %pred = and i1 %cmp1, %cmp2
+  br i1 %pred, label %if, label %else
+
+if:
+  call void @foo1()
+  ret void
+
+else:
+  ret void
 }
\ No newline at end of file
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -461,6 +461,9 @@
          QUERY( (y & ~mask = y) =>
                 ((x & ~mask = y) <=> (x = y OR x = (y |  mask)))
          );
+         QUERY( (y |  mask = y) =>
+                ((x |  mask = y) <=> (x = y OR x = (y & ~mask)))
+         );
       */
 
       // Please note that each pattern must be a dual implication (<--> or
@@ -503,6 +506,28 @@
         }
       }
 
+      // Pattern match a special case:
+      /*
+         QUERY( (y |  mask = y) =>
+                ((x |  mask = y) <=> (x = y OR x = (y & ~mask)))
+         );       
+      */
+      if (match(ICI->getOperand(0),
+                m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
+        APInt Mask = *RHSC;
+        if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
+          // If we already have a value for the switch, it has to match!
+           if (!setValueOnce(RHSVal))
+             return false;
+ 
+           Vals.push_back(C);
+           Vals.push_back(ConstantInt::get(C->getContext(),
+                                           C->getValue() & ~Mask));
+           UsedICmps++;
+           return true;
+        }
+      }
+
       // If we already have a value for the switch, it has to match!
       if (!setValueOnce(ICI->getOperand(0)))
         return false;


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