Shader JIT: Fix off-by-one error when compiling JMPs

There was a mistake in the JMP code which meant that one instruction at
the destination would be skipped when the jump was taken. This commit
also changes the meaning of the culprit parameter to make it less
confusing and avoid similar mistakes in the future.

src/video_core/shader/shader_jit_x64.cpp

@@ -653,7 +653,7 @@ void JitCompiler::Compile_IF(Instruction instr) {
     FixupBranch b = J_CC(CC_Z, true);
 
     // Compile the code that corresponds to the condition evaluating as true
-    Compile_Block(instr.flow_control.dest_offset - 1);
+    Compile_Block(instr.flow_control.dest_offset);
 
     // If there isn't an "ELSE" condition, we are done here
     if (instr.flow_control.num_instructions == 0) {
@@ -667,7 +667,7 @@ void JitCompiler::Compile_IF(Instruction instr) {
 
     // This code corresponds to the "ELSE" condition
     // Comple the code that corresponds to the condition evaluating as false
-    Compile_Block(instr.flow_control.dest_offset + instr.flow_control.num_instructions - 1);
+    Compile_Block(instr.flow_control.dest_offset + instr.flow_control.num_instructions);
 
     SetJumpTarget(b2);
 }
@@ -691,7 +691,7 @@ void JitCompiler::Compile_LOOP(Instruction instr) {
 
     auto loop_start = GetCodePtr();
 
-    Compile_Block(instr.flow_control.dest_offset);
+    Compile_Block(instr.flow_control.dest_offset + 1);
 
     ADD(32, R(LOOPCOUNT_REG), R(LOOPINC)); // Increment LOOPCOUNT_REG by Z-component
     SUB(32, R(LOOPCOUNT), Imm8(1)); // Increment loop count by 1
@@ -717,12 +717,12 @@ void JitCompiler::Compile_JMP(Instruction instr) {
     SetJumpTarget(b);
 }
 
-void JitCompiler::Compile_Block(unsigned stop) {
+void JitCompiler::Compile_Block(unsigned end) {
     // Save current offset pointer
     unsigned* prev_offset_ptr = offset_ptr;
     unsigned offset = *prev_offset_ptr;
 
-    while (offset <= stop)
+    while (offset < end)
         Compile_NextInstr(&offset);
 
     // Restore current offset pointer

src/video_core/shader/shader_jit_x64.h

@@ -61,7 +61,7 @@ public:
     void Compile_MAD(Instruction instr);
 
 private:
-    void Compile_Block(unsigned stop);
+    void Compile_Block(unsigned end);
     void Compile_NextInstr(unsigned* offset);
 
     void Compile_SwizzleSrc(Instruction instr, unsigned src_num, SourceRegister src_reg, Gen::X64Reg dest);