[PATCH] Added InstCombine transformation for combining two instructions icmp ult/ule/uge/ugt (ashr/lshr (Const2) %A), (Const1)

[David Majnemer]

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1125
@@ +1124,3 @@
+        } else {
+          Result = getConstantIfGreater(true);
+        }
----------------
This should be handled by InstSimplify.

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1136
@@ +1135,3 @@
+               I.getPredicate() == I.ICMP_ULE) {
+      Result = getConstantIfGreater(false);
+    }
----------------
As should this.

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Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1159
@@ +1158,3 @@
+    if (AP1.ugt(AP2)) {
+      Result = getConstantIfGreater(false);
+    } else if (!IsAShr || !AP2.isNegative()) {
----------------
And this.

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Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:2695-2713
@@ -2593,16 +2694,21 @@
 
-    if (I.isEquality()) {
-      ConstantInt *CI2;
-      if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) ||
-          match(Op0, m_LShr(m_ConstantInt(CI2), m_Value(A)))) {
+    ConstantInt *CI2;
+    if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) ||
+        match(Op0, m_LShr(m_ConstantInt(CI2), m_Value(A)))) {
+      if (I.isEquality()) {
         // (icmp eq/ne (ashr/lshr const2, A), const1)
         if (Instruction *Inst = FoldICmpCstShrCst(I, Op0, A, CI, CI2))
           return Inst;
+      } else if (I.isUnsigned()) {
+        // (icmp ugt/uge/ult/ule (ashr/lshr const2, A), const1)
+        if (Instruction *Inst = FoldUICmpCstShrCst(I, Op0, A, CI, CI2))
+          return Inst;
       }
-      if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
+    } else if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
+      if (I.isEquality()) {
         // (icmp eq/ne (shl const2, A), const1)
         if (Instruction *Inst = FoldICmpCstShlCst(I, Op0, A, CI, CI2))
           return Inst;
       }
     }
 
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This code would be more general if you use `m_APInt` instead of `m_ConstantInt`.

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:2702
@@ -2600,1 +2701,3 @@
           return Inst;
+      } else if (I.isUnsigned()) {
+        // (icmp ugt/uge/ult/ule (ashr/lshr const2, A), const1)
----------------
Can you just make this `if`, I think it makes the control flow a little simpler.

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:2707
@@ -2601,2 +2706,3 @@
       }
-      if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
+    } else if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
+      if (I.isEquality()) {
----------------
Why is this `else if` now?  It should be fine as `if`.

http://reviews.llvm.org/D5518