SpeculativeExecution: fixed ingoring free execution

Summary:
After updating cost model in AMDGPU target (47a5c36b37) the pass started to
ignore some BBs since they got all instructions estimated as free.

Reviewers: arsenm, chandlerc, nhaehnle

Reviewed By: nhaehnle

Subscribers: jvesely, wdng, nhaehnle, tpr, hiraditya, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74825

llvm/lib/Transforms/Scalar/SpeculativeExecution.cpp

@@ -279,9 +279,6 @@ bool SpeculativeExecutionPass::considerHoistingFromTo(
     }
   }
 
-  if (TotalSpeculationCost == 0)
-    return false; // nothing to hoist
-
   for (auto I = FromBlock.begin(); I != FromBlock.end();) {
     // We have to increment I before moving Current as moving Current
     // changes the list that I is iterating through.

llvm/test/CodeGen/AMDGPU/speculative-execution-freecasts.ll

@@ -0,0 +1,30 @@
+; RUN: opt < %s -S -mtriple=amdgcn-unknown-amdhsa -speculative-execution \
+; RUN:   -spec-exec-max-speculation-cost 1 -spec-exec-max-not-hoisted 1 \
+; RUN:   | FileCheck %s
+
+; CHECK-LABEL: @ifThen_bitcast(
+; CHECK: bitcast
+; CHECK: br i1 true
+define void @ifThen_bitcast(i32 %y) {
+  br i1 true, label %a, label %b
+
+a:
+  %x = bitcast i32 %y to float
+  br label %b
+
+b:
+  ret void
+}
+
+; CHECK-LABEL: @ifThen_addrspacecast(
+; CHECK: addrspacecast
+; CHECK: br i1 true
+define void @ifThen_addrspacecast(i32* %y) {
+  br i1 true, label %a, label %b
+a:
+  %x = addrspacecast i32* %y to i32 addrspace(1)*
+  br label %b
+
+b:
+  ret void
+}