Extend store merging to support the 'if/then' version in addition to if/then/else.
Extend store merging to support the 'if/then' version in addition to if/then/else.

This sinks the two stores in this example into a single store in cond_next.  In this
case, it allows elimination of the load as well:

        store double 0.000000e+00, double* @s.3060
        %tmp3 = fcmp ogt double %tmp1, 5.000000e-01             ; <i1> [#uses=1]
        br i1 %tmp3, label %cond_true, label %cond_next
cond_true:              ; preds = %entry
        store double 1.000000e+00, double* @s.3060
        br label %cond_next
cond_next:              ; preds = %entry, %cond_true
        %tmp6 = load double* @s.3060            ; <double> [#uses=1]

This implements Transforms/InstCombine/store-merge.ll:test2


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@36040 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,chubbymaggie/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,llvm-mirror/llvm,apple/swift-llvm,chubbymaggie/asap,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm,chubbymaggie/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,dslab-epfl/asap