Make jump threading substantially more powerful, in the following ways:

1. Make it fold blocks separated by an unconditional branch.  This enables
   jump threading to see a broader scope.
2. Make jump threading able to eliminate locally redundant loads when they
   feed the branch condition of a block.  This frequently occurs due to
   reg2mem running.
3. Make jump threading able to eliminate *partially redundant* loads when
   they feed the branch condition of a block.  This is common in code with
   lots of loads and stores like C++ code and 255.vortex.

This implements thread-loads.ll and rdar://6402033.

Per the fixme's, several pieces of this should be moved into Transforms/Utils.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60148 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/JumpThreading/thread-loads.ll

@@ -0,0 +1,34 @@
+; RUN: llvm-as < %s | opt -jump-threading -mem2reg -simplifycfg | llvm-dis | grep {ret i32 1}
+; rdar://6402033
+
+; Test that we can thread through the block with the partially redundant load (%2).
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin7"
+
+define i32 @foo(i32* %P) nounwind {
+entry:
+	%0 = tail call i32 (...)* @f1() nounwind		; <i32> [#uses=1]
+	%1 = icmp eq i32 %0, 0		; <i1> [#uses=1]
+	br i1 %1, label %bb1, label %bb
+
+bb:		; preds = %entry
+	store i32 42, i32* %P, align 4
+	br label %bb1
+
+bb1:		; preds = %entry, %bb
+	%res.0 = phi i32 [ 1, %bb ], [ 0, %entry ]		; <i32> [#uses=2]
+	%2 = load i32* %P, align 4		; <i32> [#uses=1]
+	%3 = icmp sgt i32 %2, 36		; <i1> [#uses=1]
+	br i1 %3, label %bb3, label %bb2
+
+bb2:		; preds = %bb1
+	%4 = tail call i32 (...)* @f2() nounwind		; <i32> [#uses=0]
+	ret i32 %res.0
+
+bb3:		; preds = %bb1
+	ret i32 %res.0
+}
+
+declare i32 @f1(...)
+
+declare i32 @f2(...)