Made SCEV's UDiv expressions more canonical. When dividing a

recurrence, the initial values low bits can sometimes be ignored.

To take advantage of this, added FoldIVUser to IndVarSimplify to fold
an IV operand into a udiv/lshr if the operator doesn't affect the
result.

-indvars -disable-iv-rewrite now transforms

i = phi i4
i1 = i0 + 1
idx = i1 >> (2 or more)
i4 = i + 4

into

i = phi i4
idx = i0 >> ...
i4 = i + 4


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137013 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/IndVarSimplify/iv-fold.ll

@@ -0,0 +1,56 @@
+; RUN: opt < %s -indvars -disable-iv-rewrite -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n:32:64"
+
+; Indvars should be able to fold IV increments into shr when low bits are zero.
+;
+; CHECK: @foldIncShr
+; CHECK: shr.1 = lshr i32 %0, 5
+define i32 @foldIncShr(i32* %bitmap, i32 %bit_addr, i32 %nbits) nounwind {
+entry:
+  br label %while.body
+
+while.body:
+  %0 = phi i32 [ 0, %entry ], [ %inc.2, %while.body ]
+  %shr = lshr i32 %0, 5
+  %arrayidx = getelementptr inbounds i32* %bitmap, i32 %shr
+  %tmp6 = load i32* %arrayidx, align 4
+  %inc.1 = add i32 %0, 1
+  %shr.1 = lshr i32 %inc.1, 5
+  %arrayidx.1 = getelementptr inbounds i32* %bitmap, i32 %shr.1
+  %tmp6.1 = load i32* %arrayidx.1, align 4
+  %inc.2 = add i32 %inc.1, 1
+  %exitcond.3 = icmp eq i32 %inc.2, 128
+  br i1 %exitcond.3, label %while.end, label %while.body
+
+while.end:
+  %r = add i32 %tmp6, %tmp6.1
+  ret i32 %r
+}
+
+; Invdars should not fold an increment into shr unless 2^shiftBits is
+; a multiple of the recurrence step.
+;
+; CHECK: @noFoldIncShr
+; CHECK: shr.1 = lshr i32 %inc.1, 5
+define i32 @noFoldIncShr(i32* %bitmap, i32 %bit_addr, i32 %nbits) nounwind {
+entry:
+  br label %while.body
+
+while.body:
+  %0 = phi i32 [ 0, %entry ], [ %inc.3, %while.body ]
+  %shr = lshr i32 %0, 5
+  %arrayidx = getelementptr inbounds i32* %bitmap, i32 %shr
+  %tmp6 = load i32* %arrayidx, align 4
+  %inc.1 = add i32 %0, 1
+  %shr.1 = lshr i32 %inc.1, 5
+  %arrayidx.1 = getelementptr inbounds i32* %bitmap, i32 %shr.1
+  %tmp6.1 = load i32* %arrayidx.1, align 4
+  %inc.3 = add i32 %inc.1, 2
+  %exitcond.3 = icmp eq i32 %inc.3, 96
+  br i1 %exitcond.3, label %while.end, label %while.body
+
+while.end:
+  %r = add i32 %tmp6, %tmp6.1
+  ret i32 %r
+}